Who Is Clayton on The Odd Couple? That's Potsie From Happy Days
In the same episode (tonight): Mindy from Mork & Mindy. It's a special episode honoring Garry Marshall. Happy Days and Mork & Mindy were both Marshall shows.
Also in the episode: Ron Howard, Donny Most, Marion Ross, Penny Marshall and Cindy Williams.
Wait! Not "The Fonz"? (Henry Winkler) That can't be right, can it? I'll bet he's a mystery guest or something.