Evil-Lyn is an evil witch who is the main assistant for the main villain Skeletor in the 1980s He-Man animated series.
She is the only female member of the evil crew, and she is a witch who aids Skeletor as his second-in-command with her powers of darkness. She is vastly more intelligent than Skeletor's other minions, and while she admits that she is not as powerful as Skeletor, she readily confesses that she hopes to seize her master's powers and lord it over Eternia herself one day. Thus, she has worked completely independent of Skeletor on multiple occasions. Her trademark is the magic wand crowned with a crystal ball, but Evil-Lyn typically generates magic without the assistance of any instruments.
She sometimes works on her own, even betraying skeletor. In the episode "Teela's Triumph", she is the first one that Teela ambushed, and captures, leaving her tied and gagged to a pilar. In another episode, they are both forced to team up against a greater menace.
Although her background is never mentioned in the series, the series bible explains she was once a scientist from Earth called Evelyn Powers, who was on board Marlena Glenn's space craft before it crash-landed on Eternia. Evelyn had been insanely jealous of Marlena for being chosen over her to pilot the shuttle. When the ship crashed as the result of an explosion from Skeletor's homeworld of Infinita, Evelyn wound up on Infinita, where the evil powers of that world turned her knowledge of science into sorcery to aid Skeletor. This origin is used in a storybook entitled New Champions of Eternia but was unpopular with the show's writers and therefore never alluded to in the cartoon.