- "Take her to the moon for me, okay?"
- —Bing Bong's last words before he fades away
Bing Bong was the tritagonist in Inside Out.
Bing Bong was Riley's imaginary friend that existed within her mind. He was created by her when she was three. As a result, he was somewhat naive in both his appearance and personality. For instance, he does not know how to read everything. Bing Bong's body is mainly made of cotton candy. Shape-wise, he was part cat for the tail and whiskers, part elephant for his trunk and ears, and part dolphin, though the latter is not so obvious. He cried candy when he was sad.
Riley used to play with Bing Bong in all sorts of games when she was three. However, she stopped when she was four, and since then, Bing Bong had been out of work and errant. He mostly stayed around Imagination Land, collecting happy memories he liked in a bottomless bag.
He greatly missed the time when he was best friends with Riley, and was desperate to not be forgotten. Bing Bong's last link to Riley was his "rocket", a wagon that was meant to take Riley to the moon. It ran on song power, meaning its rainbow rockets would light up when his song "The Bing Bong Song" was sung.
After Joy and Sadness are ejected from Headquarters and get lost in Long Term Memory, they stumble upon Bing Bong. He is initially afraid, but when Joy presents herself, he is thrilled to meet her. Bing Bong, who has been forgotten by everyone for a long time, is more than happy to help them, more so when Joy tells him she will put him back in business when she gets back to Headquarters. He proposes that they take the Train of Thought that will lead them directly to Headquarters, and shows them the way.
He leads Joy and Sadness to a dark room, which he thinks is a shortcut, claiming that the scripture above the door reading "D-A-N-G-E-R" means "shortcut". However, as soon as the three are inside, the room closes and reveals itself to be Abstract Thought, a place that reduces everything to abstract concepts. Bing Bong and the others escape, but when they get out, the Train of Thought has left.
Bing Bong leads them to the second closest station, at Imagination Land (which he is practically the mayor of). As they are there, they witness drastic changes in what Riley thinks about, with more childish things being toppled down. In the process, Bing Bong's precious wagon rocket is thrown into the Memory Dump, which puts him in a profound despair. Joy tries to cheer him up, but in vain. Then, Sadness talks to him and, by getting him to express his grief, comforts him. Bing Bong, happy again, brings them to the Train of Thought.
However, the train stops as Riley goes to sleep. Bing Bong, Joy, and Sadness go to Dream Productions to try and wake her up. In trying to do so, they bring the dream currently being filmed in total chaos. Bing Bong shows himself to try to remind Riley of him, but he is arrested and imprisoned in Subconscious. He is rescued by Joy and Sadness, who also free Jangles, one of Riley's worst fears, to wake her up.
Finally, the three of them can board the running Train of Thought. Bing Bong finds on board a recent memory of Riley, and is surprised to see how she has grown, concerned that she won't fit in his wagon rocket. However, the train is quickly destroyed by the destruction of Honesty Island. When Family Island crumbles down, Bing Bong falls with Joy into the Memory Dump as he was trying to catch her. There, he is terrified to notice that he slowly fading and on the verge of disappearing.
Together, Joy and Bing Bong decide to use Bing Bong's wagon rocket to blast off and reach the surface. They sing as hard as they can, but they can't get high enough. They try again louder and faster, but still don't make it. As Joy begins to lose hope, Bing Bong glances at his fading left arm, and taking a decision, asks that they try one more time. This time, sacrificing himself so that Riley can be saved, Bing Bong lets go and falls back down as the wagon rocket takes off, letting Joy succesfully escape the Dump in the now lighter cart. Bing Bong, happy to have been helpful once more and accepting that his time has passed, asks Joy to take Riley to the moon for him, before fading away with a final smile.
- The film was originally going to feature a whole slew of "imaginary friends", as characters from Riley's early childhood that were now refugees living in a place called "Hobo Camp". In addition to Bing Bong, these included Mrs. Scribbles, who was a stick figure, and "Corner Sun", who was literally a quarter of Sun as kids would draw in the corner of their drawings. Ultimately, this storyline was condensed to just Bing Bong.
- After being asked why Bing Bong is made of cotton candy, Pete Docter simply stated, "I like cotton candy."
- Bing Bong's illiteracy might come from the fact that Riley created him at a very young age.
- Bing Bong's overall fate is very similar to what Woody narrowly avoided in Toy Story 3, both literally and figuratively. Literally in the sense that Bing Bong disintegrates into nothing in a heap after falling in to the Memory Dump, similar to how Woody avoided the incinerator's fiery core. Figuratively in the sense that Bing Bong is no longer needed due to the child outgrowing him, similar to Woody's fears through Toy Story 3, and a subconscious fear through most of the Toy Story franchise.
- His tail is very similar to the Cheshire Cat's tail from Alice in Wonderland.
- Although he has faded away, it's quite possible that Riley still remembers him, according to The Bing Bong Book. At the end of that book, Bing Bong finds Storybook Land, where three Bing Bongs from books Riley wrote when she was younger appear to join him for tea.
- While saying his last line, "Take her to the moon for me, okay?", his voice actor Richard Kind was crying.