Booster first debuted in the direct-to-video film, Buzz Lightyear of Star Command: The Adventure Begins. He is initially a simple janitor at Star Command, but he dreams of becoming a space ranger. He is shown to have memorized the ranger handbook, to the extent that he can cite exactly which section a rule is in.
Booster is a native of the planet Jo-Ad, which is an agricultural planet. He is shown to be naive, sweet, and a bit shy, but he also possesses a great deal of raw strength. He is also shown to be in awe of Buzz.
When Harvest Season begins on his planet, he has an urgent need to return, lest the more monstrous portions of his species' ancestry pop up and cause him to wreak havoc. This frenzied state is useful for harvesting the crops.
Booster is introduced as a janitor that Buzz saves from being fired. Booster is eager to become a space ranger, but so far, hasn't gotten the opportunity. At one point, he overhears the other rangers talking, but when he asks what is going on, he is told simply that it is ranger business, and so he leaves, depressed.
Booster later meets XR, who was led to Booster by the Little Green Men. XR offers Booster a "VIP Tour" of Buzz's spacecraft, and while role-playing, become stowaways. Buzz has taken his spacecraft and is pursuing Mira Nova, who is attempting to bypass Emperor Zurg's defenses. Buzz discovers Booster and XR, and is about to fire Booster, when they learn that Zurg has used the Uni-Mind, a sphere that telepathically links the LGMs, to mind control all of Star Command.
Buzz goes off alone to confront Zurg, but Booster, XR, and Mira follow him, and rescue him. They confront Zurg, but Zurg is able to flee using an escape pod. However, Booster and XR are able to capture Warp Darkmatter, Zurg's accomplice. Due to his role in the rescue, Booster is made a space ranger, and is recognized alongside Buzz and the others for their heroism. Booster then joins "Team Lightyear" a team made up of himself, Buzz, Mira, and XR.
In the TV series, Booster, now a space ranger, accompanies Buzz and Team Lightyear in the battle against Emperor Zurg. Booster contributes raw strength to the team.
Toy Story comics
Booster was incorporated into the Toy Story universe in "The Return of Buzz Lightyear", published in issues 0-3 of Boom! Studios' Toy Story comic book. In the story, which appears to take place between the first two films (as Jessie, Bullseye and The Aliens are noticeably absent), Andy Davis' grandmother mistakenly sends him a second Buzz Lightyear action figure, so Andy and his mother take it to the Toymania store and exchange it for an action figure of Booster. However, unbeknownst to Andy, the new Buzz got in a fight and then switched places with his original Buzz, prompting Woody, Slinky Dog, Rex, Hamm, Mr. Potato Head and Rocky to travel all the way to Toymania and rescue their friend. They take Booster with them since they figure that he, being from the toy store himself, knows the directions.
Like Buzz in the first Toy Story film and Utility Belt Buzz in Toy Story 2, Booster initially does not realize he is a toy and instead believes himself to be the TV character he is based on, though he is noticeably written as being more cowardly than he was in Buzz Lightyear of Star Command. Booster eventually figures out he is actually a toy after arriving at the toy store and hiding in a pile of teddy bears, but takes the revelation better than Buzz did in the first movie.
At the end of the story, Booster is still among Andy's toys, but this creates a plot hole in relation to the movies. While it can be assumed that Booster was eventually sold in a yard sale (presumably to another kid) after Andy outgrew his toys prior to the events of Toy Story 3, his absence from Toy Story 2 is never explained. Further highlighting this problem, Booster also notably does not appear in Boom!'s later two Toy Story comic arcs, "Some Assembly Required" and "Toy Overboard".