Arthur Fonzarelli. No doubt. Although Mork from Ork was strong enough to launch not just a character but an entire career.
You might say Trapper John from M.A. S. H. too, but he was played by different actors in the movie, the series, and the spinoff.
I liked Trapper John MD.
Elliot Gould player Trapper John McIntyre in the movie MASH
Wayne Rogers player Trapper John in the TV Show MASH
Pernell Roberts player Trapper John in the Spin-off “Trapper John, MD”
From MASH, I was thinking either Radar O'Reilly or Margaret Houlihan. Or even Max Klinger, originally a one-episode throw-in who became a major member of the team.