Evil Jim is an evil copy of Earthworm Jim. He was created by a horrible toxic waste/photocopier accident, and claims to be Jim's exact opposite in every way. This is most obvious in their speech patterns: while Jim likes to use big fancy words and monologue when he addresses someone, Evil Jim keeps everything brief and to the point. Where Jim would say "Egads, danger is afoot!" Evil Jim would say "Something bad will happen." However, when Jim points out that he hates losing, and his twin should therefore enjoy it, Evil Jim responds, "Don't be so literal-minded."
Evil Jim looks exactly like Earthworm Jim except for a green coloration, slightly pointier digits, and neglected teeth. Evil Jim states he enjoys the taste of orange juice after brushing his teeth (which Earthworm Jim hates).
He is apparently motivated by a desire for destruction, though on several occasions he has expressed loneliness as well. He nearly succeeded in winning the heart of Princess What's-Her-Name by reading poetry to her, but was interrupted at the last minute by Jim. Evil Jim actually once succeeded in creating opposites of Peter Puppy and the Princess. He also accidentally created copies of Queen Slug-for-a-Butt, Evil the Cat, and Professor Monkey-For-A-Head when he dropped the copy gun. However, the results were not what he had expected - Evil Peter transforms into a good monster, and Evil Princess is vain and weak, the Queen's opposite is motherly, Good the Cat is nice and chases Evil in an attempt to kiss him, and Monkey Professor-For-A-Head is pretty much what would happen if the Professor and the Monkey swapped brains and they become friends out of mutual concerns - and he ended up imprisoned once more. Evil Jim, like his counterpart, is voiced by Dan Castellaneta (in a style similar to Krusty the Clown, Megavolt and e.t.c., also a villain).
Evil Jim was created for the Earthworm Jim animated series and does not appear in the first two games; however, Evil Jim was the primary antagonist in the later Earthworm Jim: Menace 2 the Galaxy game for the Game Boy Color.