4. Ricky Gervais
Star of British sitcom "The Office", Ricky Gervais also guest starred in an episode of Family Guy, as irritable dolphin "Billy Finn" in the season 10 episode "Be Careful What You Fish For". When Peter goes out fishing for a, erm, Mercedes-Benz after hearing a cargo of them sank, he instead encounters Billy who fetches him a hood ornament. Peter reluctantly agrees to return the favour by letting Billy stay at his house due to his estrangement with his ex-wife, but the annoying dolphin soon outstays his welcome and drives everyone up the wall. In a bid to free himself from Billy, Peter reunites him with his ex-wife after returning him to the ocean.