Film: The Emperor's New Groove (2000)
Actor: Eartha Kitt
Yzma is pretty... ugly. As an evil villain she has schemes just as dastardly as the rest - and equally just as daft as the rest too. She could easily give Wile. E. Coyote a run for his money in the stupid plan stakes.
On the positive side, her megalomaniacal ways are often muted by her henchman Kronk - but his reason often falls on deaf ears. Perhaps if she had, the Empire wouldn't now be run by a llama that vaguely resembles its former leader.
Eartha Kitt isn't a name that springs to most people's mind when they think of comic actresses. In truth, that's because she's not. She's a singer who has happened to have appeared in a few films. Remember the song "Santa Baby" before it was redone by a million different artists? Yeah, that was Eartha Kitt originally.
Film-wise she has still had a reasonable career with over 30 acting credits to her name. Most recognisable of these are her turn as Yzma from Emperor's New Groove (and the direct-to-video sequels), Bageera in The Jungle Book sequel and Madame Zeroni in Holes (2003).