RIP Martin Mull

His character Barth Gimble that hosted "Fernwood Tonight" and "America Tonight" actually came from the dreadful sitcom "Mary Hartman, Mary Hartman" on which he played the same character.
So in some way, that horrid sitcom actually launched his career (if you've never seen it, consider yourself lucky and don't bother trying to hunt it down anywhere).
Fernwood Tonight/America Tonight was brilliant, though. I loved that show!

I'd bet he guest-appeared in at least 100 different sitcoms and cartoons over the last 40-50 years. A testament to how well he was known in the industry is how many times he appeared playing himself on different shows rather than as a random character (though obviously, most of the time it was as a random character).