LOS ANGELES (AP) — Don Rickles kept the nice inside, his friends say. Lucky us.

Offstage, the self-described "shy and frightened kid" was invariably kind and caring, fellow celebrities said after his death Thursday at age 90.

So are many other worthy people. But Rickles, only Rickles, could leave that sweet man offstage and turn into a smirking, hairless attack dog who chewed out fans and famous pals alike with brutal insult after insult.

Everyone ate it up, because he practiced an equal-opportunity brand of humor that targeted people by race, religion, appearance and anything else he could find to mock.

And because his career was born in the 1950s, when racist and sexist broadsides delivered by white male comedians were OK, and he got grandfathered in for the remainder.

And because he really knew how to craft and deliver a line, including on the fly, and did it with chutzpah — Yiddish for nerve — and a leavening, even charming dash of bad-boy glee.

And because candor, including his sharp-edged version, can be powerful.

In one of his many "Tonight Show" appearances, Rickles teased Johnny Carson that he should retire after nearly 20 years as host. Carson replied that he liked to hang on to a job, not bounce around like Rickles.

The firecracker was lit.

"Look right there (the camera), and let America know you're a millionaire and don't need them," Rickles shot back.

Carson laughed.

Speaking at a roast, with Dean Martin seated on one side and Sammy Davis Jr. on the other, Rickles told them: "You're Catholic, I'm a Jew, and Sammy, you're black. I'm sorry."

Davis laughed.

That meant we all had license to laugh, too. When Rickles would sense backlash from the audience, though, he had a ready reply: "Don't write letters, folks. We cover them all."

The tributes flowed after kidney failure claimed his life Thursday, a month shy of his May 8 birthday.

Billy Crystal tweeted that his death was "a giant loss." Bob Newhart and his wife, Ginnie, said Rickles' title was "The Merchant of Venom" but he was "one of the most sensitive human beings we have ever known."

Renee Taylor, who played Rickles' wife in the 1993 TV sitcom "Daddy Dearest," called him a delight to work with.

"Every day I looked forward to coming to the set and being insulted," she said. "When Don did an impersonation of me, I felt he got me and I felt the love, too."

Samuel L. Jackson posted this on Instagram: "Farewell to a comedic legend & dear friend, Don Rickles. I know you're cracking them up in the Great Beyond!"

Rickles didn't start out wanting to master the art of insult comedy. As a self-described insecure youngster, he settled on an acting career and enrolled in New York's American Academy of Dramatic Arts.

When that dream faltered, he tried comedy at small hotels in New York's Catskill mountains and in rundown nightclubs. He found his voice at a strip joint in Washington, D.C.

"The customers were right on top of you, always heckling, and I gave it right back to them," he recalled in an interview.

A half-century-plus career ensued, including headline gigs at casinos and nightclubs from Las Vegas to Atlantic City, New Jersey, talk-show appearances and roast after roast.

He kept his hand in acting with movies, acting opposite big names in movies like "Run Silent, Run Deep" (Clark Gable) and Martin Scorsese's "Casino" (Robert De Niro), and a short-lived couple of TV shows, "The Don Rickles Show" in 1972 and "C.P.O. Sharkey" from 1976-78.

But did any of them top his voice performance as crabby, aggrieved Mr. Potato Head in the animated "Toy Story" movies? Nope. Or energetically dishing out zingers even in his later years? No again.

Rickles, finally, seemed to accept that.

"I did have somewhat of a career. I did some good movies," he said in 2007. "On the whole, I think that (movies) and Broadway are the two things that I would have liked to have a little more of. But I'm happy with my career."