In the Legion of Super Heroes episode "Legacy", the young Superman meets Alexis (voiced by Tara Strong), the "richest girl in the galaxy" in the 31st century, who also has a knack with machinery and access to her own corporation's powerful technology. A beautiful redhead who wears a purple jumpsuit (echoing Lex Luthor's original hair color and classic costume), Alexis starts out as a friend of Superman, but is scorned when he refuses to neglect his duties with the Legion in favor of spending time with her.
To get rid of the "competition" for Superman's time, Alexis equips the Scavengers with cutting-edge weaponry and, after luring Superman away with a fake distress call, personally dons a large, advanced battlesuit, and leads an attack on the remaining Legion members. Superman returns in time to aid his friends and makes it clear to Alexis in no uncertain terms that he wants her out of his life. Alexis resolves to fight Superman, her reasoning being that if he will not be her friend, he will not be anybody else's either and she blasts him. Superman tries to warn her that she cannot hurt him and he overloads the barrel of Alexis' gun and her suit blows up. Superman pulls her free in time to save her life, but in addition to the injuries she sustained from the blast, all of her hair is seared off.
Instead of showing gratitude, Alexis is incensed. In the final scene, she has recovered and appears to be regrowing her hair while in prison. Her prison uniform displays the name "Luthor" written in the Interlac alphabet. While rebuilding her butler/bodyguard in her cell in Takron-Galtos, Alexis ominously states that she is actually grateful to the Legion, since they helped her realize her potential as a supervillainess. She is seen again in the season one finale where the Legion break out the Fatal Five, locked in her cell as she sticks her tongue out at a passing Superman. She's last seen in the second season premiere, her hair still not regrown, escaping with a crowd of inmates.
Young Lex makes an appearance in the tie in comic Legion Of Super Heroes In The 31st Century #13. Making his Metropolis debut, Superman saves Lex and the surrounding crowd from Lex's own out of control prototype battle suit. Though this version of Lex does not yet show hostility towards the Man Of Steel, Brainiac 5 warns Superman to keep an eye on Lex.