Known for his blond hair and neat mustache, Mull was born in Chicago, grew up in Ohio and Connecticut, and studied art in Rhode Island and Rome.

He took his first steps in show business as a songwriter: in 1970 he wrote the semi-hit “A Girl Named Johnny Cash” for the singer Jane Morgan.

He combined music and comedy in a number that he brought to trendy Hollywood clubs in the 1970s.

“In 1976, I was a guitarist and comedian performing at the Roxy on the Sunset Strip when Norman Lear came in and heard me,” Mull told the Associated Press in 1980. “He cast me as a wife beater in 'Mary Hartman, Mary Hartman.' Four months later, I got my own show.”

His time on the Strip was immortalized in the 1973 country-rock classic “Lonesome LA Cowboy,” in which the Riders of the Purple Sage honored him along with music greats Kris Kristofferson and Rita Coolidge.

“I know Kris, Rita and Marty Mull hang out at the Troubadour,” the song goes.

In “Fernwood Tonight” (sometimes called “Fernwood 2 Night”), he played Barth Gimble, the host of a local talk show in a Midwestern town and twin of his character “Mary Hartman.” Fred Willard, a frequent collaborator with a very similar comedic flair, played his sidekick. The series was later rebooted as “America 2 Night,” set in Southern California.

As a replacement for Johnny Carson on the “Tonight Show,” he was allowed to become a real talk show host.

Mull often played slightly sleazy, somewhat slimy, and often smarmy characters, such as Teri Garr's boss and Michael Keaton's enemy in 1983's Mr. Mom. He played Colonel Mustard in the 1985 film adaptation of the board game Clue, which, like many other things Mull was in, became a cult classic.

The 1980s also saw the creation of what many consider to be his best work: A History of White People in America, a mockumentary that first aired on Cinemax. Mull co-created the show and played a 60 Minutes-style investigative reporter who investigated all things boring and mundane. Willard once again co-starred.

He wrote the screenplay and starred in 1988's Rented Lips alongside Robert Downey Jr., whose father Robert Sr. directed the film.

His co-star Jennifer Tilly said in an X-post on Friday that Mull was “such a funny, charismatic and kind person.”

In the 1990s, he was best known for his recurring role in several seasons of “Roseanne,” playing a warmer, less sleazy boss to the title character, an openly gay man whose partner was played by Willard, who died in 2020.

Mull later played private investigator Gene Parmesan on “Arrested Development,” an iconic character on a cult series, and was nominated for his first Emmy in 2016 for a guest appearance on “Veep.”

“I'm very proud of what I did on 'Veep,' but I'd like to think it's more collective, at my age it's more collective,” Mull told the AP after his nomination. “Maybe it goes back to 'Fernwood.'”

Other comedians and actors were often his biggest fans.

“Martin was the greatest,” Bridesmaids director Paul Feig said on X. “So funny, so talented, such a nice guy. I was lucky enough to star with him on The Jackie Thomas Show and loved every moment I spent with a legend. Fernwood Tonight had such an impact on my life.”

Mull leaves behind his daughter and musician Wendy Haas, whom he has been married to since 1982.