The success of the original game spawned several ports, and a sequel, "Donkey Kong Jr." In this game, Donkey Kong Junior 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. The game was developed by Nintendo R&D1 and released in August 1982. In the arcade version, Donkey Kong Jr. has to touch a key, then it moves up to the top screen. Donkey Kong Jr. has to climb to the top screen while avoiding things such as electrical wires. When he gets to the top screen, Donkey Kong Jr. will have to touch the key again, and it will move to the keyhole of one of the chains. Donkey Kong Jr. has to climb up the rope below the keyhole, while avoiding birds. When he gets to the top of the rope, one of the chains will unlock. He has to do this 4 times until he saves Donkey Kong. After that, the game will start over, at a somewhat faster pace.