GOOD GUYS GONE BAD
I like movies where an actor who has usually played good guy roles suddenly turns up as a villain. Here are some of the best of these:
Paul Newman was almost always the fair-haired boy or at worst the loveable scamp. Everyone loved him in Somebody Up There Likes Me (1956), Butch Cassidy and the Sundance Kid (1969), The Sting (1973) and many others. But in Hud (1963) he shows up as this truly awful guy, raping Patricia Neal and in general being as unlovable as a snake. 
Fred MacMurray was the caring, wonderful Dad for years in the TV series My Three Sons, and was the good guy in movies like The Egg And I (1947), The Miracle of the Bells (1948), and Fair Wind To Java (1953). But in Double Indemnity (1944) he is an insurance agent besotted with the nefarious Barbara Stanwyk and together they plot the early demise of her unsuspecting husband. 
Denzel Washington has almost always been the hero or at least the good guy in films like Glory (1989), Crimson Tide (1995), and The Bone Collector (1999). So you would figure in a cop movie he would be “good cop” but he’s definitely “bad cop” in Training Day (2001), corrupting rookie officers and anyone else in his way. He also turns out to be less than a stellar hero in Flight (2012). Actually, this guy can play most anything. 
Jack Lemmon has made a good living as the all-American boy next door in films like The Apartment (1960), Bell Book and Candle (1958), The Wackiest Ship In The Army (1960), and The Notorious Landlady (1962). But he is completely 
unsympathetic as the whiny, hopeless alcoholic in Days Of Wine And Roses (1962), dragging down everyone around him as he spirals to the bottom. 
The short, brilliant career of Heath Ledger has been marked by good guy movies like Brokeback Mountain (2005) and The Brothers Grimm (2005). Yet he becomes the quintessential villain in the Batman epic The Dark Knight (2008) as the Joker, a very unfunny character, perhaps the darkest of all Batman foes. 
And finally there is Bing Crosby, the smooth as silk crooner beloved by everyone in such films as Going My Way (1944), The Bells Of Saint Mary’s (1945), and all those mediocre Road movies with Bob Hope. Then came The Country Girl (1954) and he plays opposite Grace Kelly and William Holden as the truly awful drunk Frank Elgin. In fact, he was so good as this bad guy that he won the Oscar!
All of the movies in this article are available on DVD and for streaming. Too many to rate for appropriate ages!