Comet is a Golden Retriever who was introduced on the show in season three. He was born to a dog named Minnie. He was played by Buddy.
He debuted in the season three episode "And They Call It Puppy Love". Comet's mother, Minnie, ran away from her home and somehow ended up in the Tanners' backyard while she was pregnant. She gave birth to a litter of puppies (including Comet) on Jesse's bed. Her owner, Frank Flood then arrived to get her shortly after she gave birth and was so grateful that they had taken such good care of her and her puppies, he allowed them to keep one. After Joey convinced Danny to let them have a puppy, D.J. told Michelle to pick which one they would keep, so she picked the one Jesse was holding and they named him "Comet" (after shooting down Michelle's suggestion it be named after her, and Stephanie's suggestion it be named 'Mr. Dog' after Mr. Bear). By the end of season three, Comet had fully grown to the full size of an average Golden Retriever, something D.J. mentions to Michelle in the season four episode "One Last Kiss". Michelle was trying to keep Sparky, saying that Comet was already too big for her, but D.J. mentions that pets like Comet grow much faster than humans like them. She goes on to explain that Comet has already stopped growing, and when Michelle stops growing soon, it will seem that he is getting smaller while she is getting bigger, even though in reality he's (roughly) the same size as her.
In the season eight premiere, "Comet's Excellent Adventure", Michelle constantly reminds Jesse, while he is busy talking on the phone, that it is his turn to walk Comet. In the heat of the moment, he inadvertently tells her to do so herself. She is only 7 years old and not very strong, so Comet escapes from her. Since she is not allowed to cross the street by herself, she only follows him to the end of the sidewalk. When Stephanie finds out about this, she gives her sister a lecture about how walking a dog alone is a big responsibility. He spends the day exploring the city with a female collie after chasing a "hot dog car". Danny and Becky happen to be broadcasting their talk show live at the time that he is informed about Comet's disappearance. He abruptly announces the news to the viewers, and lets Michelle say some words to Comet as well. When he sees her message on a television in the window of a local store, he immediately runs back home and is reunited with the family.
Comet died some time after Full House ended, but in his lifetime he sired at least one litter of puppies. One of the dogs from this litter was named Comet Jr. (gender unknown), who then either sired or gave birth to a litter of puppies between the finale of Full House and the premiere of Fuller House. This litter included Comet Jr. Jr., who was adopted by Steve Hale and can be seen in Fuller House. In the episode "Our Very First Show, Again," Comet Jr. Jr. had her own litter of puppies, making Comet a great-grandfather. Two of these puppies were named by Max Fuller, one of them as Comet Jr. Jr. Jr., in order to continue the Comet naming tradition, and the other as Cosmo, who became the Fullers' family dog.
Buddy was also known for playing the title character in Air Bud, and was featured in the episode "Air Jesse" (season 8). He was born in early 1988 and died in his sleep from cancer on February 10, 1998 at age 10. His story is told in the 2012 book Go Buddy!, written by his owner Kevin DiCicco.