Saul Goodman should probably get a mention. He was a secondary character so strong in Breaking Bad that he's carried his own series for multiple seasons.

True. Testify. Thanks

Community has so many - Todd, Leonard, Garrett.

21 from The Venture Bros and his arc across the series is really up there.

I think his sister Tamar is better

Neil's evolution, from Fat Neil to Real Neil With Pipes Of Steel to Vicky's Boyfriend And A Crusader Against Bear-Related Offensiveness, was painted in broad strokes and thrilling to watch.

Leo (Tommy Chong) on That 70's Show.

Creed Bratton

That would be Andor now streaming on DISNEY+

I'd submit that Nick Swardson's "Terry", from RENO 911, is the finest secondary/tertiary character ever written.

Does John Astin as Buddy from Night Court count? I loved when he would show up and we'd find out his latest developments, or another bit of his backstory.

I have an answer, and that answer is a person. And the name of that person, is Perd Hapley.

Creed Bratton. My bad was working off of memory and thanks to the Redditor that drew my attention to itand was cool about it.

Excellent choice now I want to binge Reno 911

That last exchange with 24: "Why did you buckle up???" "I DON'T KNOW!!!" was so perfect.

With Living 24, of course, he had a lot of conversations with Ghost 24.