Here’s a really fun interview with Phil Hartman, from a 1996 episode of Late Night with Conan O’Brien.
His Ed McMahon impression includes the catchphrase ‘Hiyo’, which is clearly the inspiration for Hank Kingsley’s ‘hey now’ from The Larry Sanders Show. In fact, in this moment between he and Larry, I love that when he is fumbling around for Larry’s catchphrase, he does Johnny Carson’s golf swing.