Billy Finn is a talking dolphin that befriends Peter Griffin in "Be Careful What You Fish For".
When Peter and the guys try to salvage a sunken Mercedes-Benz after hearing a news report of a cargo of them sinking, Peter half-heartedly promises a favor to a Billy that helps him recover a hood ornament. Billy decides to take Peter up on his offer and see what things are like on dry land. Peter is amused at Billy's sense of humor at first, but Billy soon begins to wear out his welcome. When Peter finally agrees to ask Billy about moving on, Billy proposes getting Peter a second hood ornament which stops Peter in his tracks. When Peter discovers part of his problem is his estrangement from his ex-wife Joanne, Peter reunites the couple and gets Billy to return to the ocean.
Billy also has a crowd scene cameo and is identified by name in "No Giggity, No Doubt".
Billy joins several other animals of the show as well as the cast in singing "Blue Shadows On The Trail" in "Wild Wild West".
Billy is voiced by Ricky Gervais.