Who was character Evil in willow the wisp cartoon series?

There is no character named "Evil" in the *Willow* cartoon series. The series is based on the 1988 film of the same name, and features characters like Willow Ufgood, Madmartigan, Elora Danan, and General Kael.

It's possible you're thinking of a different series or are misremembering the character's name. Can you provide more details about the character or the series you're thinking of?