Fun fact: Mario was a villain at one point

In the sequel to the original Donkey Kong arcade title, Donkey Kong Jr. Whereas in the first game, you played Mario (or by his original name "Jumpman") and had to rescue his girlfriend Pauline who was captured by Donkey Kong, in the sequel, the roles are reversed. You play the title character whose father has been kidnapped by Mario, who he must rescue. It is the only game to date where Mario is explicitly cast as an antagonist.