Many actors appear in different episodes in the same role as recurring characters. Some actors, however, portray different characters in different episodes.
In most of the cases, the portrayed characters are minor characters not related to each other and the episodes in which they appear are in different seasons so that the similarity is not obvious to the viewer.
On the other hand, a similarity may be intended, for example when Tom Welling portrays Clark's father Jor-El in his youth or when Kristin Kreuk portrays Lana's ancestor Margaret Isobel Thoreaux or her great-aunt Louise McCallum. Further examples are Connor Stanhope and Lucas Gabreel, who both portray a youth version of Lex Luthor as well as of Conner Kent who was a clone of Lex, or Aaron Ashmore who portrayed Jimmy Olsen as well as his younger brother James Bartholomew Olsen.
Among the actors portraying different characters are (in the order of their first appearance):
- Aaron Ashmore's twin brother Shawn Ashmore had portrayed Eric Summers in season 1 and 3 before Aaron first appeared on screen in season 6. The similarity between the two characters, however, was never mentioned or explained.
- Some episodes show an alternative reality or universe where even main cast members portray an alternative character. These characters, however, are not in fact different characters, but rather the same character under different circumstances (such as Clark Luthor in some Season Ten episodes)
- In Season Six's episode "Noir", Jimmy has a dream or vision of himself as a star reporter in 1940. In this dream or vision, also the 1940s versions of Clark, Lana, Lex, Lionel, and Lois appear, all portrayed by the same actors as in the main timeline.
- Clones of other characters may also be portrayed by the same actor as the original character.
- If a character somehow takes possession of another character, for example as a Kryptonian vessel, the actor portraying the possessed character also portrays the character who has taken over possession. Michael Rosenbaum, for example, who generally portray Lex also portrays Zod in the episodes "Vessel" and "Zod" while Zod has taken possession of Lex.
- A similar case are shapeshifters who can assume the shape of another character. Eric Johnson, for example, who generally portrays Whitney Fordman, also portrays Tina Greer while she has assumed Whitney's shape in "Visage".