Donkey Kong Jr. (ドンキーコングJR., Donkī Kongu Junia^?) is a 1982 arcade-style platform video game by Nintendo. It first appeared in arcades, and, over the course of the 1980s, was later released for a variety of platforms, most notably the Nintendo Entertainment System. The game's title is written out as Donkey Kong Junior in the North American arcade version and various ports to non-Nintendo systems. Its eponymous star, Donkey Kong Jr., also called simply Junior or abbreviated as DK Jr., is trying to rescue his father Donkey Kong, who has been imprisoned. Donkey Kong's cage is guarded by Mario, in his only appearance as a villain in a video game. This game is the sequel to the video game Donkey Kong, which featured Mario as the hero and Junior's father as the villain.

Mario, known beforehand as Jumpman, has incarcerated Donkey Kong after re-capturing him in Donkey Kong. Donkey Kong Jr. must save his father from Mario by putting the key or keys in the stage into all of the locks. Mario attempts to stop DK Jr. by releasing the many animals he controls to knock DK Jr. off the vines and platforms. DK Jr. defeats Mario if the player completes the fourth stage by putting all six keys in their locks, making the floor disappear. DK Jr. catches Donkey Kong while Mario falls onto the ground.