Billy the Tracker
In the 80s Sonny Landham had some impressive acting credentials: after starting out in porno flicks, the granite-faced star went on to appear in classic blockbusters such as 48 Hours and Predator, in the latter of which he played enigmatic muscleman tracker, Billy. Unfortunately, as a politician in the 2000s he was much less successful.
His attempt to win the governorship of Kentucky was cut short after he "called for genocide against Arabs and referred to them as 'ragheads'" (to quote Wikipedia).
This resulted in him being fired by the Libertarian Party of Kentucky, as even they aren't crazy enough to endorse that kind of crap. He has now gone back to his previously prolific career as an actor, but now appears in straight-to-DVD dreck.
You would have thought a Native American descendent would be more sensitive about a subject like genocide...
Dillon
Carl Weathers made his reputation playing rough-and-tough characters like Dillon in Predator and, even more notably, Apollo Creed from the Rocky film series.
Sadly, his action film star declined after the 90s as he began to increasingly move into TV and comedy roles, and the once-great action star and former football player now appears chiefly in self-parodying parts in commercials and TV comedies (although he did land a funny recurring role as himself in Arrested Development).
True he may not quite be a "nobody," but he's nothing like the face of 80s action that he once was, and mocking your earlier roles isn't really what you want to end up doing with your acting career. It's all a far cry from his gut-wrenching death in Rocky IV...
Mac
Bill Duke's psychotic expression is so convincing it made him the scariest good guy in Predator, a movie which of course also featured Jesse Ventura, future governator Arnold Schwarzenegger, and an 8-foot tall invisible psychopath, as well as the aforementioned Carl Weathers and Sonny Landham (was that film cursed???).
He also did some sterling "acting" as co-henchman to Vernon Wells in the earlier action movie Commando. However, since the 90s Duke hasn't had many roles in movies and has gotten by mainly on TV guest appearances and directing his own critically panned movies.
Shockingly, he was responsible for Sister Act 2, a film which would have been better if they'd called it "The Fugees Unplugged" and cut out everything except the bits with Lauryn Hill singing.