What is the name of Riley's imaginary friend?

Riley’s imaginary friend in Inside Out is named Bing Bong.

Bing Bong is a colorful, part-elephant, part-cat, part-dolphin creature who lives in Riley’s mind. He represents an imaginary companion from her early childhood and becomes Joy and Sadness’s guide when they are stranded in the distant regions of Riley’s mental world.

Richard Kind provides Bing Bong’s voice. The character is more than a comic sidekick: his story reflects how childhood memories and imaginary relationships can fade as a person grows older. His candy-themed rocket, which runs on “whoo-hoo!” power, is one of the film’s memorable details.

Viewers sometimes confuse Bing Bong with one of Riley’s five emotions, but he is not an emotion. He is a long-standing creation of Riley’s imagination. His emotional importance becomes especially clear near the film’s climax, when his friendship with Joy helps Riley’s emotions find their way home.