Jimmy Damon died of cardiac amyloidosis, a rare heart disease, on his 75th birthday Saturday, his wife, Marilyn Damon, told the Chicago Tribune.
He had been living at Chicago's Rush University Medical Center's Horizon Hospice and Palliative Care.
Damon -- born Jimmy Demopoulos in Memphis, Tenn. -- was a fixture at Chicago nightclubs, concert halls, charity events and award presentations for four decades.
He sometimes sang the national anthem at Wrigley Field, home of baseball's Chicago Cubs, and was the opening act for big-time comedians, including George Burns and Bob Newhart, his daughter, Dana Damon-Trentadue, told the Chicago Sun-Times.
The street outside the Chicago condo he called home for decades is now called Jimmy Damon Way.
"I sing as though there's 100,000 people in front of me," Damon told the Sun-Times in 1999.
"That's what I'm about," he said. "If there's just one person in the room, that might be the right person. You came to hear me sing, you're going to get it, babes. I don't hold back."
This tendency could make him slightly overbearing in the 1970s, early in his Chicago career, Damon acknowledged to the Tribune.
"I was still learning how to be an entertainer, how to connect with an audience, how to put things together," he told the newspaper in 1998. "In those days, I was the lounge lizard that was becoming Jimmy Damon."
It was in the early 1970s that Murray caught Damon's lounge-lizard act at a now-defunct Chicago club, Damon and many others said. Murray was part of the Second City improvisational theater troupe at the time.
Damon's act was the inspiration for Nick the Lounge Singer, one of Murray's most popular recurring characters during his late 1970s three-year "Saturday Night Live" tenure.
The character sang current songs in a drawn-out, schmaltzy manner.
Nick always had a different "seasonal" last name, such as Summers or Springs, and would always sing his heart out, even at unfortunate gigs such as airport bars and dives.
Damon told the Tribune he didn't mind that Murray spoofed him.
"I wasn't upset," he said in the interview. "I just wish he'd sent me a check. He owes me a lot of money."
Damon -- who wore tight leather pants and an open-chested shirt beneath a leather jacket with fringe and rhinestones when Murray saw him -- later wore a tuxedo.
"But he always kept his cowboy boots," Damon-Trentadue told the Sun-Times.