Jojo Jr. is the Monkey Prince of Monkey Island. He is the son of Jojo Sr., the monkey from the first game who helped Guybrush get to the Giant Monkey Head by clinging on to the nose of a totem pole. According to Jojo Jr. his father died of starvation when Guybrush forgot to train him to let go of the pole. When Jojo was burying his father near the Giant Monkey Head he was affected by its strange Voodoo Magic that gave him an immense understanding of the world around him, as well the ability to talk.

By the fourth game, Monkey Island has become infested with monkeys due to the 'great summoning' (foreshadowed within the game with a number of monkeys' disappearances). Jojo meets Guybrush when he is once again left on Monkey Island. During the game the player must challenge and beat Jojo in Monkey Kombat to receive his bronze hat, which can be used to create a gigantic Ultimate Insult talisman. Jojo Jr. is noticeably more difficult than other monkeys, partially because in Monkey Kombat he doesn't quit and won't stop even if he's losing.

Jojo also comes to Guybrush's assistance in his epic last confrontation with LeChuck and Ozzie Mandrill on board the Giant Monkey Robot. After the battle Jojo and the other monkeys leave for parts unknown.