What's the name of Michael Knight's evil twin?

The answer is: Garthe Knight. To clarify, calling Garthe a “twin” is a little bit of a stretch. They do have the same face, but technically they’re not brothers. Garthe is the son of Wilton Knight — the dude who came up with the whole idea of turning Micahel Long into Michael Knight. Their faces are the same because Wilton basically used Garthe’s face for him — which in turn caused Garthe to see Michael as a replacement and caused a burning rage in his heart.There’s actually a pretty complicated backstory here, but I guess the writers didn’t feel like keeping Garthe around — or maybe Hasselhoff was losing his mind playing both characters. Either way, Garthe died in his second and final appearance in Knight Rider, never to be heard from again.Source