George Costanza claimed to have saved a whale while pretending to be a marine biologist.
In the season-five episode "The Marine Biologist," Jerry tells George's former classmate Diane that George has become a marine biologist. Jerry invents the claim because George was left out of their college alumni magazine, while Jerry was mentioned. George reluctantly agrees to maintain the lie when Diane becomes interested in him.
The deception reaches its absurd climax when George and Diane encounter a beached whale surrounded by people searching for a marine biologist. George is pushed into helping. Later, he gives Jerry and the others a dramatic account of the rescue, saying he was washed onto the whale and reached into its blowhole. He claims he pulled out a golf ball, which had been struck into the ocean by Kramer.
The whale story is often remembered as though George saved a dolphin or another sea creature, but the episode specifically makes it a whale. The climactic monologue was reportedly added late in production by Larry David and Jerry Seinfeld, and Jason Alexander delivered it so effectively that the first take was used.