- "I have this feeling that you'll never fulfill your great destiny until you meet your greatest challenge." - Tess Mercer to Clark Kent, Eternal
The relationship between Clark Kent and Tess Mercer had its ups and downs over the years. First it was suggested of a romantic relationship between them and she wanted to know his secret but later they developed a great friendship.
This relationship is referred to as "Cless" by fans. 
- "No one has the right to choose who lives and dies. I was beginning to think that you were different from Lex. I was wrong." - Clark Kent
- "The difference is that he turned his back on you. But I still believe. I understand that if everyone was more like you, the world would be a better place. But the truth is that it's out of your hands now. You can't avoid your fate." - Tess Mercer
Tess first met Clark when he saved her from a bus explosion caused by Bette Sans Souci. After Tess was taken to the paramedics, she insisted that she was fine and went back to the Daily Planet where she introduced herself to Clark as the new CEO of LuthorCorp. During their conversation, Tess revealed to Clark that Lex Luthor had told her all about him. She wondered if Clark had any suggestions on where to find Lex, but Clark claimed he had no idea. Tess refused to believe him and planned to keep a close eye on him. Clark was instantly able to see the Luthor-like traits in Tess and warned her not to let her life be consumed by the job like Lex did.
When Oliver Queen was poisoned, Clark investigated what could be the cause. Clark's investigation led him to Tess when he discovered that Oliver and Tess had met before and that LuthorCorp may have the antidote. When Clark pleaded with Tess for help, she seemed to want to be of assistance but told Clark that the antidote was in Brazil and it would not be able to get to Metropolis in time to save Oliver. At this point, it is clear that Tess did not know about Clark's powers, as he was able to superspeed to Brazil to get the antidote. Clark then realized that the person that had poisoned Oliver was also after Tess, so Clark supersped to her rescue without Tess' knowledge.
Tess and Clark crossed paths again, as Tess became interested in the Crystal of Knowledge that was found in the Arctic Circle. Tess asked Clark if he had ever seen it but he lied to her. Tess was very distrustful of Clark at this point and was becoming increasingly intrigued by him. Tess eventually revealed to Clark that she knew that he was the last person to see Lex alive. This made Clark even more cautious of Tess.
Clark became angry with Tess when he found her at Lana Lang's ransacked apartment. He suspected Tess was behind it but she quickly explained everything from Lana's awakening from her Brainiac-induced coma: Tess and other LuthorCorp employees under Lex's orders, forced Lana to break up with Clark at gunpoint. This only increased Clark's anger and he pushed her against a wall. Tess was clearly shaken by this and apologized, saying Lex had claimed it was for Lana's own good. Tess was clearly driven by Lex's orders and, due to Clark's irreparable relationship with Lex, Tess and Clark's relationship was clearly strained.
Tess, after reading Lex's journal on Clark, tried to learn exactly what made Lex so obsessed with him. She requested that Clark join her on a business trip and during their flight Tess began to reveal parts of her past in the hope that Clark would also open up. However, Clark was more interested in finding out what Tess had read about him in Lex's journal and tried to get her drunk. Their heart-to-heart was interrupted by an explosion on the plane, which Tess had orchestrated to force Clark into exposing his powers. Clark managed to knock Tess out and jump to safety without exposing his secret, much to Tess's annoyance. She remained suspicious of Clark's account of the events, as he claimed to have found a parachute. Clark on the otherhand seemed to have softened to Tess and promised not to tell anyone of what she told him on the plane. Tess replied that Lex was right about Clark not having "a bad bone in his body". Tess felt that Clark was the "prince who came to [her] rescue". Tess felt close enough to Clark to tell him about her physically abusive father.
Tess eventually revealed to Clark that she knew his secret, having read Lionel's journal. Clark continued to deny it despite Tess's insistence, reawakening Clark's distrust of Tess. She attempted to reassure him by insisting that she was not like Lex. It was only when Tess's assistant Eva Greer disguised herself as Chloe Sullivan and witnessed Clark's powers that Clark was more open about his abilities to Tess. She clearly admired him, although she disagreed with his approach to stopping Doomsday and tried to manipulate him into becoming the hero she knew he could be.
- "I confided in you, Clark. You confided in me. You revealed your powers. You know I haven't told anyone your secret." - Tess Mercer
- "Only to sell me out to Zod and the others." - Clark Kent
When Tess was attacked at the Luthor Mansion by zombies, Clark went with Lois to interrogate her. They discuss Tess's reason for being institutionalized at the hospital and Clark remarked that Tess was a strong woman who is not intimidated easily. Lois thought that Tess was crazy, but Clark defended her. After being greeted by an zombie-infected Tess that threw Lois across the room, Clark restrained Tess so the doctors could sedate her.
Since Zod and his army arrived on Earth, Tess kept an eye over them, and when she learned that they were looking at the Blur, she seemingly allied with them in order to protect Clark.
When Clark´s Kryptonian father was on Earth, he was taken by armed men sent by Tess. Tess told Jor-El that he needed to protect his son, and convinced him to pose as the Blur to mislead the Kandorians. Clark found out Tess had Jor-El and confronted her. He grabbed her by the neck, lifting her several feet off the ground and Tess admitted she was waiting for Clark to tell her his identity, but hoped it was because he trusted her. Tess told him that Zod's men took Jor-El from the Luthor Mansion and that she put a tracking device in his clothes so they can find his location. This action caused Clark's confidence in Tess to disappear completely.
After Tess kidnapped Lois in order to examine her memories of the missing three weeks, Clark arrives at Tess's lab and she tries to blame Stuart for her actions, but Clark shoves her aside, rendering her unconscious in order to save Lois.
Clark arrived at the Planet to find Tess snooping through Lois's desk. He forced her to hand over Lois's notes and Tess walked away, saying it was difficult to have a nosy girlfriend. Tess and Zod later talked about which side she was on as he accused her of being with Clark who was working for the Kandorians freedom. Tess pointed out that Clark would soon rule over his people.
Clark confronted Zod about who killed Jor-El and Zod said it was Tess. Angry, Clark accidentally persuaded himself to go after Tess. He super-sped her from her office at the Planet and decided to take revenge for his father... by killing her. Clark said the solar tower would take away his powers and Tess is shocked, as she didn't know. Before Clark could kill her, however, he was stopped by Chloe with kryptonite.
Later, Tess found out that Oliver was Green Arrow, Clark barged in on their argument and took Tess to a high rooftop in Metropolis. Terrified of being thrown from the rooftop, Tess told Clark that Oliver wasn't the real target—Watchtower was.
After Tess went underground, she had some of her scientists experiment on John Corben with a red kryptonite heart. After he escaped, Clark went down to the lab and accidentally inhaled red kryptonite. Chloe went to investigate and teamed up with Tess to find Clark and stop him from wreaking havoc. They found and reprogrammed Corben to go find and stop him and Tess later used the information to find the Fortress of Solitude.
Clark later went to the Fortress to speak to Jor-El only to find out that Zod had destroyed the crystal console. After Zod left, Clark found Tess half burned on the ground and immediately took her to get help at Metropolis General Hospital.
Clark visited Tess in MetGen where she revealed she did what she did to save Clark from Zod. Clark had the Book of Rao but it was useless because the console in the Fortress is gone. Tess told him the Kandorians built a crystal energy source when they attempted to turn the sun red and that she salvaged it from the destroyed solar tower and moved it to his crow's nest above the city and that it could power the book.
She told him she was trying to atone for her sins and that Clark was the only one who can save them but that he had run out of time, for the war had already begun.
- "Thanks. I'm use to handling things on my own." - Tess Mercer
- "You're a part of my team." - Clark Kent
Clark arrived at Cadmus Labs, found the lab in ruins and to his surprise, Tess handcuffed in another room. She told Clark that she didn't know how she got there. She then told Clark that one of Lex's clones had done the damage caused and destroyed the other clones. Clark was skeptical at first but Tess told him the clone left her alive to give Clark a message to meet him in Lawson's Field. Clark released Tess from her cuffs before going off to face the clone.
After an assassination attempt to Clark's new partner was made, Clark went through some journalist identity files at Tess's office at the Daily Planet to try to found more about the girl. Tess walked in and Clark told Tess that something weird was going on with Cat. Clark mentions the bullet found in the car with the visible letters and Tess did a computer search and located the possible assassin. Tess later discover that the bullet lodged inside the car had the name "CLARK KENT" embedded on it and showed it to Clark, helping him to save Cat.
When Lois was possessed by the spirit of Isis, Tess offered her help and knowledge on how to exorcise Isis' spirit from Lois. Keen to get her back, Clark accepted her help much to Oliver's dismay who still didn't trust her. In the end Tess' information was what saved Lois' life. Clark and Oliver both realize how helpful she could be and made her the new watchtower coordinator. She thanked them and left before being overcome with joy. Oliver asked Clark if they think could trust her and said they'll soon find out.
Tess discovered that Clark and Oliver were both tagged and being tracked by Rick Flag and the Suicide Squad with tattoos underneath the skin. Tess was working on a way to remove the tattoos as well as figure out what Flag's plans were. Clark suggested he was Flag's target but Tess explained that he was a vigilante sympathizer and that he would want to recruit him before he ever wanted to kill him. Tess and Clark were then able to discover that Rick Flag planned to kill Sam Lane for his support in the Vigilante Registration Act.
Clark visited Tess at Watchtower after getting a call. Tess told Clark a dream she had, and how a box with a sticker under it came to her. Clark peeled the sticker that said "Happy Birthday," and found another label underneath that led him to discover St. Louse's Orphanage, run by Granny Goodness. They both go to Saint Louise's, claiming to be doing a story for the Daily Planet. Granny Goodness greets them and has the girls sing, but then Clark hears something with his superhearing and claimed to go to the car to get a notebook so then he could investigate farther. Clark is captured by the Female Furies while Granny locks Tess in her old room she once had as seen in her dream. Tess manages to escape but only to get captured by the Furies. Clark later managed to escape Granny's grip and supersped to find Tess. He finds her hanging from the ceiling, saved her and knocked out the girl responsible. Tess thanked him for his help and admitted that she's used to looking after herself. Clark assured her that he wasn't going to abandon a teammate.
Tess helped Clark in finding Oliver after he signed up for the VRA and taken to a holding facility by Slade Wilson. Tess gave Clark information about the facilities and that they hold anyone with any type of abilities. After Oliver was rescued, Clark welcomed Lois as part of the team at Watchtower and Tess did as well. Oliver arrived Clark informed them about the coming darkness on Earth and how its infected people like Slade. He also explained to Tess, Oliver, and Lois that it feeds on people's fears and doubts, making Tess realize the fears and doubts that she has.
Clark called Tess and told her to met him at Cadmus Labs. At Cadmus Labs, Clark revealed to Tess that there was one Lex clone unaccounted for, and that he discovered a lead-lined room. Clark deduced that the Lex clone was in there. Tess tried to convince Clark to give this Lex a second chance, but Clark stated that Luthor blood was poison. When Clark and Tess walked into the messy room they saw a small bed, as well as the crest for the House of El. Clark noticed a book on the desk, and found a note addressed to Tess from Lex saying that he's "all grown up". Clark confronted Tess about hiding the clone, and said that she betrayed his and Oliver's trust. While Tess tried to explain he noticed a Kryptonian artifact in her purse and began to question her on why she had it. As she tried to explain Clark activated the mirror box and was immediately transported to an alternate reality where Lionel Luthor had raised him instead of the Kents.
Clark found Tess in the loft waiting for him. She started to kiss him much to his surprise and Clark resisted. Tess replied with "Don't worry, our daddy won't find out" to which Clark was surprised to the revelation that she was indeed a Luthor. Clark revealed to Tess that he was not who she thinks he is. Tess then discovered that Clark's scar was gone, and realized that he used the mirror box and expressed anger for Clark Luthor for lying to her. Clark asked Tess what was going on, and Tess revealed that he was in a darker alternate universe, and that Clark Kent's earth was about to get a huge awakening.
Clark eventually managed to make the switch back to his universe to find Tess, Oliver and Lois standing over him with kryptonite weapons. Clark managed to convince Lois it was really him and allowing Tess and Oliver to lower their weapons. Clark later met with Tess at the mansion and apologized for what he said about the Luthor blood being poison, and that it's not blood that makes the Luthors bad, but how Lionel raised them. Tess told Clark that she was upset with Lionel for giving her up. Clark assured her that she was lucky enough not to have been raised by Lionel. Tess told Clark the reason why he didn't tell him about the Lex clone because she didn't want anyone to take away the only real family she’s ever had and that the Lex clone had her fooled. She went on to say that the clone was just as smart as Lex if not smarter. She explained to Clark that he wouldn't be found until he wanted to be. Clark said to Tess that when he does come out, they would face him together, and reassured her that she will never be alone again.Tess threw Clark and Lois an engagement party. Tess, Lois, and Emil Hamilton were all later taken in for questioning by the government for their involvement with the heroes. Tess and Emil were being taken to a warehouse and Clark saved them. Clark learned from them that Slade Wilson had taken over and that Lois was missing.
Tess informed Clark that the Lionel from Clark Luthor's world had arrived in this world. Oliver then came in and told them that Lionel is with Alexander (the Lex clone) and taking back LuthorCorp. Clark said he would find a way to deal with the Luthors. Alexander later held Clark and Tess at gunpoint with a kryptonite gun at Clark's loft. Tess managed to get to Alexander and allowed threw the gun away allowing Clark to recover.Tess was at Clark and Lois's bachelor/bachelorette party along with Oliver, Chloe, and Emil. Everyone drank some champagne that was spiked with magic and ended having a wild night. Clark found Tess, who was dressed as a June Cash look-alike showgirl along with Emil who was dressed like Elvis sharing the spotlight to a country rock song onstage at the Ace of Clubs. He then saw some police officers ply Emil off the stage and arrest him on charges for stealing an armored vehicle. Tess instantly figured out it was Clark who stole the vehicle. Tess was later popping hangover pills at Watchtower, as her, Clark, and Chloe looked for leads as to what happened the night before. They found out that the armored car could be traced by sounding the alarm and having Clark catch the signal with his super hearing. His superpowers proved unnecessary, when the alarm beeped from inside his pocket. He traced the signal from the car back to no other location than his barn. Later Tess, Clark, and everyone else enjoyed the amusing footage from the night before as Emil had recorded all of it.
Tess awaited at the farm for Clark to arrive home. When he did, she told him of Alexander's progression, and that Clark should be the one to look after him. Clark was very hesitant of this for Alexander was a clone of Lex and extremely unpredictable. Tess was about to explain to Clark that something else was happening to him, but before she could, they both heard a crash coming from the barn. They ran out to find the cause of this noise and found Alexander, now with Black hair, lifting a tractor over his head. Clark was stunned by this, to which Tess explained that not only did Alexander have Lex's DNA, but half of it was Clark's. Clark agreed to take in Alexander who was now named Conner and teach him how to control his abilities. Tess returned later to see how Conner was progressing with Clark. They began to talk about Conner still having of parts of Lex inside of him and him not remembering. Both thought it would be best if they didn't tell Conner about that part of him to which Conner overheard and sped off.
Tess informed Clark and Lois that Slade had escaped the Phantom Zone and was found in an alleyway. Clark set out to investigate by going into the Zone himself. Clark used the help of Tess to create energy in the Crystal of El to open a portal to the Zone. Clark had planned with Tess to destroy the gate to prevent any more prisoners from escaping. Oliver ended following Clark into the Zone and Clark informed Ollie of his and Tess's plan once inside. Lois managed to changed Tess's mind and Clark and Ollie managed to make it out of the Zone on their own.
Clark and Lois found that Stargirl was controlled by a mysterious device and Tess analyzed the mind control diode at Watchtower and discovered that it was created by Winslow Schott, for a group of villains known as Marionette Ventures. Later, Tess and Clark received news from Courtney that their transportation to Stryker's Island was ready, just as a super-powered, mind controlled Lois arrived at Watchtower and attacked Clark. Tess, in a panic, counted down the seconds to sundown when Clark would get his powers back, hoping that he could stall Lois until then to which he did.
Tess tried fantically to phone Clark to warn him that Darkseid's Apokolips was coming. On her way to Smallville she was intercepted and taken by Lionel's men. Clark later retreived Tess's phone learned that Lionel had captured her. Since Tess had been tracking Lionel, Clark went to where he believed he was at the Luthor Mansion and learned from a resurected Lex that Tess was fine. Tess later made the ultimate sacriface for Clark as Lex killed her and she infected Lex with a neurotoxin causing him to forget all memories of Clark and his secret. In her dying words she stated that Clark prevented her from turing into Lex and that he was responsible for her redemption thus proving her loyalty to Clark over Lex.
- "Hey there stranger. We're sorry we took so long." - Clark Kent
- "Thank you." - Tess Mercer
At LexCorp Plaza, Lex heads towards his office only to find Superman with Green Arrow and Lois Lane revealing they are here to take Tess back. Lois slaps Lex knocking him unconscious. At Watchtower, Clark, Lois and Oliver stands patience as Emil downloads a grateful Tess into a computer system making her a hologram.
- Tess and Clark's first interaction mirrors Clark and Lex's first interaction where Clark rescued Tess from a bus that had just exploded while Clark rescued Lex from his Porsche which he had driven off a bridge.
- Producers originally intended for Tess to develop a romantic interest in Clark. This is alluded to when Zod uses the metaphor "Are you in bed with the blur?" and Tess gives a sultry comeback. Later, this scrapped storyline was used with Tess' doppelganger being in a relationship with Clark Luthor and Clark Luthor revealed that she has feelings for Clark but she knows he will never reciprocate them, a fact Clark Luthor uses to try and manipulate her. In the end of the series, Tess confessed her feeling to Clark and wanted to help him save the world from the Kandorian army for redemption.
- Due to the fact that Conner Kent shares both Clark and Lex's genetics, the two of them are somewhat like siblings as they are connected to Conner by blood relation with Clark as Conner's "brother" and Tess as Conner's "sister" but different like in the alternate universe that Clark Luthor and Tess Luthor are "brother & sister" due to being raised by Lionel Luthor.
|Clark Kent in Smallville|
|Tess Mercer in Smallville|