Mortlegax loves being evil and tries hard to act like it. He appears to be strict but also very fair and willing give others a chance. Mortlegax takes evil very seriously and always has to see details. He loves his evil laugh, complete with background thunder and lightning.
Role in the series
Mortlegax is first seen complementing Jumba on his experiment work via computer screen. At first, Jumba is pleased, but then Mortlegax reveals they've been getting reports of Jumba's experiments not acting evil. He says they can't risk the scandal if Jumba has gone good, so he will have to revoke his membership. Jumba tries to get him to reconsider, but Mortlegax refuses. Lilo then intervenes by standing up for Jumba, and Mortlegax assumes that she is his evil assistant, but Lilo points out that it's actually Stitch. Mortlegax says that he is in Jumba's quadrant next Tuesday visiting his Aunt Bootsie and offers a deal. If Jumba can convince him personally that he is still evil, he will extend Jumba's membership, and Lilo agrees to his deal.
When Mortlegax arrives at the Pelekai residence, Lilo and Stitch try to trick him into thinking that Jumba was still evil by showcasing several of his evil experiments on the Internet. Lilo and Stitch's facade is successful at first until Mortlegax notices a screen of Experiment 262 (Ace) rescuing a neighbor's cat from a house that was on fire. As a result, Mortlegax revokes Jumba's membership and promptly leaves.
Mortlegax's role in the plot of the original storyboard version of "Ace" is identical, with him still revoking Jumba's membership as in the final version, but the turnout of events in the second half of the episode differs.
In the original storyboards, Mortlegax seemed to be impressed by the facade as in the final version, but he needed more convincing, so he makes Jumba take him around Kokaua Town to see more of the experiments at work, while Lilo, Stitch, Pleakley, and several experiments begin to work on a bigger charade at a secluded spot on the beach. On the streets, Jumba shows Mortlegax Slushy scaring two pedestrians and freezing the road to make them fall, but Ace comes to the pedestrians' rescue and melts the ice on the road. Mortlegax becomes suspicious of the heroic experiment, but a worried Jumba falsely claims that the experiment is just a new crossing guard and moves Mortlegax away to avoid further suspicion.
When the two aliens arrive on top of some craggy rocks looking over the secluded beach, at a distance far away enough to avoid making out the revealing details of the facade, Lilo and Stitch pull off their illusion with Kixx launching Cannonball into the Pacific Ocean to form a massive tidal wave with Pleakley, Spike, Splodyhead, and several rag dummies being the "victims". However, Ace comes in to "save" Pleakley and the dummies, confirming Mortlegax's beliefs from earlier. He gets disgusted by the sight of heroism as Stitch intervenes and traps Ace in a containment capsule. Thanks to the capture, however, Pleakley gets trapped by the dummies as they pile on top on him, putting him in the wave's wake. Mortlegax becomes pleased at the sight of the "meaningless" Pleakley's impending doom, but an incensed Jumba defies Mortlegax and decides to rescue his friend, even after Mortlegax says that Jumba will be expelled from E.G.O. for doing so. Jumba succeeds in rescuing Pleakley, and an insulted Mortlegax tears his evaluation papers, officially expelling Jumba from E.G.O., and leaves in disgust.