- "You may want to change yourself to impress Clark Kent, but we both know... don't we? Deep down, you'll always be a Luthor." - Lionel Luthor to Tess Mercer, Scion
- "I'm upset that he threw me away... As grotesque and sordid a family tree as I've just inherited, I... Wasn't good enough." - Tess Mercer about Lionel Luthor, Luthor
Tess was born Lutessa Lena Luthor, Lionel Luthor's illegitimate daughter (from an affair with Pamela Jenkins) and second child. Lionel gave up Lutessa at the age of nine to the St. Louise's Orphanage ran by Granny Goodness. Lutessa's memories about her birth parents and childhood so far were removed by Granny. Lionel located a home for his daughter and threatened Granny to close the orphanage down if she had resisted Lionel's orders. Granny complied and removed Lutessa's memories of the orphanage before sending her to her new parents. Lutessa was adopted by the childless Mercers in Louisiana.
Tess began looking into Davis Bloome's background only to discover he didn't have one. She thought she had reached a dead end, until she stole a journal of Lionel's that she claimed to have stolen. She stated that it was about a boy that came down the very same day the meteor shower happened and that she did not believe the boy came down alone. Tess explained to Davis that Lionel sent a search party for a traveler who was told would come from a fire from the sky but didn't realize that there were two boys that fell to earth that day, the Traveler and Davis. After Davis put her in the hospital, Tess is visited by Clark Kent and she revealed that she had Lionel's journal and that he wanted to possess the Traveler, which was why he was in Smallville on the day of the meteor shower. She talked about the painting of a two headed creature - Naman and Sageeth - and how there was another boy who came to the planet with Clark that was destined to be his ultimate nemesis. Clark pretended not to believe Tess's story and Tess replied that Lionel took Davis, but then the boys tests didn't match what they expected of the Traveler. After five days, Lionel had Davis put out onto the street after being asked for help with Clark's adoption. Tess accused Clark of being the reason for Davis being abandoned by Lionel.
- "Time to become the Luthor you were destined to be." - Lionel Luthor to Tess Mercer, Finale, Part 2
Tess began having nightmares of her time at Granny Goodness's orphanage and received a present from Granny herself that wished her a happy birthday. Tess went back to the orphanage where Granny explained that she had Tess for the first five years of her life and then her birth parents took their daughter back and put her into a good home. Granny went on to say that they were powerful, as well as would have closed down the orphanage if Granny had fought back. Tess obtained her birth certificate from the orphanage and remembered her past when her father left her at the orphanage and thereby discovering that Lionel is her father and her mother is Pamela Jenkins. The birth certificate read her real name and Tess went to the window of the Luthor Mansion and wished herself (Lutessa) a happy birthday.
After discovering she was a Luthor, Tess was Lionel's only living heir and received a Kryptonian mirror box from a lawyer. When Clark accidently used the mirror box to teleport to an alternate universe where Lionel found and raised Kal-El as his own son Clark Luthor while Tess's counterpart had grown up knowing that Lionel was her father. While attempting to get Kent back to his kinder, gentler Earth, Tess snuck to Lionel's office in search of information about the mirror box but was caught by Lionel. Having known about Tess's plan to escape to another reality and accused her of corrupting her brother to do it, Tess defended herself saying that he was responsible for that and finally ended slapping her father after he provoked her. As Lionel called security to remove Tess, she warned him that Clark would eventually kill him. After returning to Earth-1, Clark Kent and Tess Mercer later met at the mansion and apologized for what he said about Luthor blood being poison and that it's not Lionel's blood that's bad but how the man raised them. Tess admitted to Clark that she was upset with Lionel for giving her up but Clark assured her that she was lucky enough not to have been raised by Lionel.
Tess walked into her office at the Daily Planet to find Lionel sitting at her desk. She quickly deduced that her "father" is the Lionel of Earth-2 and he explained that the world believed that Lionel simply faked his own death in this reality and now he was back to take care of his family, including his daughter. He also revealed to Tess that he knew about Alexander Luthor and knew that she abandoned him. Lionel demanded to know where he was but Tess told him she didn't know, and stated to Tess that Alexander needed his "father". Oliver Queen informed Clark and Tess that Lionel and Alexander together had taken-over LuthorCorp. Tess suggested to Clark to use the mirror box to send Lionel back to his reality, but Clark told her that he destroyed the device after he got back from Earth-2.
Determined to protect Conner Kent from Lionel, Tess found her alternate-reality father investigating at Cadmus Labs and there she showed him the “remains” of Conner. However, Tess was unsuccessful in her deception as Lionel discovered Conner is still alive. Tess continued to try and bring Lionel down and even enlisted the help of Lois Lane. Tess managed to discover that there was one document which Lionel overlooked: her adoption paper. Having proven that Lionel was not who he claimed to be, she had Lionel's liquor traced with nanoscopic tracking devices, Tess confronted Lionel, regained control of LuthorCorp, as well as had him escorted from the LuthorCorp building.
When Clark Luthor returned from his Earth, Tess was asked by her "brother" to help him so he could kill their father. Tess showed him the GPS that was tracking Lionel, and Clark set out to kill him but Tess rerouted the tracker. Clark returned knowing what she had done and couldn't find it in her to kill Lionel.
Unhinged after Tess had taken his empire from him and still desperate to restore Lex Luthor, Lionel had Tess kidnapped and brought to a lab. At the lab were body parts from Lex's destroyed clones were grafted to Lex, Lionel explained to Tess that Lex lacked a heart. Lionel intended to use Tess's heart and made it very clear he was perfectly willing to sacrifice his own daughter to have his son back, cementing the fact that he preferred Lex over Tess and that she was only good for this purpose. When his surgeons were about to perform the operation, Tess fought back and shot Lionel, proclaiming that her purpose as his daughter wasn't to be his tool. Although the attack mortally wounded Lionel and Tess left him for dead, he managed to restore Lex with the help of Darkseid.
|Tess Mercer in Smallville|
|Lionel Luthor in Smallville|