Beloved U.S. comedian Don Rickles, the curmudgeonly pioneer of insult comedy best known for his abrasive mocking, has died at the age of 90.

Rickles died Thursday morning from kidney failure at his Los Angeles home, according to his longtime publicist Paul Shefrin.

Though widely praised for his kindness, for being a loyal friend and a devoted family man offstage and when the cameras were off, Rickles became a household name in North America for his acerbic, insult-filled brand of humour that spared no one — from regular Joes to U.S. presidents to the famously hot-tempered Frank Sinatra, who became one of his champions and a close friend. 

"He was called The Merchant of Venom, but in truth, he was one of the kindest, caring and most sensitive human beings we have ever known," Bob Newhart and his wife, Ginnie — longtime friends of Rickles and his wife Barbara — said in a statement Thursday afternoon. 

"We are devastated and our world will never be the same. We were totally unprepared for this."

Born in New York, Rickles served in the U.S. navy during the Second World War and later graduated from the American Academy of Dramatic Arts.

He occasionally appeared in films over the years, including war drama Run Silent, Run DeepThe Rat Race with Tony Curtis, Pajama Party and Beach Blanket Bingo with Annette Funicello, Kelly's Heroes with Clint Eastwood, Martin Scorsese's Casino and as the voice of Mr. Potato Head in the Toy Story movies.

He was also a regular face on TV over the years, guest starring on a wide range of shows, including The Twilight Zone, The Dick Van Dyke Show, Laugh-In and Hot in Cleveland. 

After his initial acting career stalled, Rickles toiled away in the conventional standup scene. He broke through on the nightclub circuit when he found his footing heckling his hecklers and honed his act to focus on rapid-fire takedowns — comedic verbal assaults of stars, public figures, Las Vegas crowds and TV audiences.

"I think the reason that [my act] caught on and gave me a wonderful career is that I was never mean-spirited," Rickles once said. 

"Not that you had to like it, but you had to be under a rock somewhere not to get it."

Sarcastically dubbed "Mr. Warmth," Rickles' prickly performance persona led to headliner status at casinos and nightclubs across the U.S. 

He had regular guest spots on late-night TV thanks to fans Johnny Carson and David Letterman and even landed a gig at a presidential inaugural ball, where his comedic targets included Ronald Reagan, who had just been re-elected. Soon, being the target of ribbing by Rickles became a badge of honour for fans famous or not.

Rickles released a number of comedy albums, including Hello Dummy! and Don Rickles Speaks. The memoir Rickles' Book emerged in 2007, the same year John Landis directed the Emmy-winning HBO documentary Mr. Warmth: The Don Rickles Project.

An honorary member of Sinatra's Rat Pack, he grew into a beloved show business elder with time, as well as an inspiration to comics, including Joan Rivers, Sarah Silverman, Louis C.K. and Chris Rock. Some of his celebrity fans, including Jon Stewart and Jerry Seinfeld, honoured him in the 2014 Spike TV special One Night Only: An All-Star Comedy Tribute to Don Rickles.

'Don is something rare, [a] true friend, a wonderful human being. If he weren't, he would never be able to get away with being such an a--hole.'

- Robert De Niro

"Don is something rare, [a] true friend, a wonderful human being. If he weren't, he would never be able to get away with being such an asshole," quipped Robert De Niro at the televised 2014 roast.

Indeed, when asked about how he wanted to be remembered, Rickles put aside the humour.

"If people know me well, they know I'm an honest friend. I'm emotional; I'm caring; I'm loyal. Loyalty in this business is very important," ​Rickles told The Associated Press in 1993. 

Rickles continued to perform in recent years, including a continuing tour with Regis Philbin. He had postponed shows in Nevada and Florida this month and last, citing ill health.

Survivors include his wife of 52 years, Barbara Sklar, his daughter, Mindy, and her husband, and two grandchildren. He is predeceased by his son, Larry, who died in 2011. 

A private funeral is being arranged. In lieu of flowers, the family asks that donations be made to the Larry Rickles
Endowment Fund at Children's Hospital Los Angeles.

With files from The Associated Press