Notorious Empire turncoats in the lore?

I'm a big Chaos 40K fan, and I've been working on a Warriors+Daemons of Chaos army recently. However, some of the Empire models I have tempt me to play them as Chaos Marauders/Knights (painted as battleworn turncoat to the Dark Powers perhaps).

So.i was wondering, are there any notable traitor regiments or commanders who fall to Chaos in the fantasy setting I can read about?