Robert Klein, who's appearing April 5 at the Raue Center for the Arts in Crystal Lake, was the first comedian to appear in a live concert on HBO. His most recent – "Robert Klein: Unfair and Unbalanced" – aired in 2010.

Before Jay Leno, Billy Crystal or Jerry Seinfeld, Robert Klein was delivering the type of observational jokes they’d emulate.

As Leno revealed during his final episode of “The Tonight Show,” a poster of Klein was the only thing hanging in his apartment when he struggled as an aspiring comedian in the 1970s.

When Klein first began entertaining audiences more than 40 years ago, comedians were a different breed. They wore cuff links and tuxedos. They stood out.

Klein was pretty much like everybody else. His jokes weren’t one-liners. He talked about what everyone else was talking about. He made life funny.

“My material has always been organic,” he said. “I talk about life... Just like a good novel, if you make good observations, it’s universal.”

And at age 72, he’s still making life funny.

He’ll take the stage – his favorite place to be – for another one-man show at 8 p.m. April 5 at the Raue Center for the Arts, 26 N. Williams St., Crystal Lake.

It’s a show, Klein said, that might surprise people.

“After so many years in the business, I’m still a well-kept secret in person,” he said. “I’ve never been a big tour guy . . . In person, it’s a much different thing than a few minutes on [David] Letterman’s couch.”

It’s a couch he’s been on about 50 times, by the way. He’s also been on “The Tonight Show” couch quite a bit, having been invited by Johnny Carson 82 times.

He’s the type of celebrity you just know you’ve seen or heard somewhere. Because he’s been so many places.

On Broadway: Neil Simon’s musical “They’re Playing Our Song” and Wendy Wasserstein’s “The Sisters Rosensweig.”

On comedy albums: “Child of the Fifties,” “Mind Over Matter,” “New Teeth” and “Let’s Not Make Love.”

On television: “Law and Order,” “Sisters,” “Royal Pains,” to name a few of the numerous series he’s appeared in.

In movies: “How to Lose a Guy in 10 Days,” “Two Weeks Notice,” “The Owl and the Pussycat,” “Primary Colors,” “Hooper” and many more. (He likes to joke about the 1999 film “Goosed” he appeared in with Joan Rivers. “I have a routine about making love to her in the movie. In the orgasm, we brought in a stunt man from California,” he said.)

Lately, he said, he’s played a lot of fathers, including Sandra Bullock’s in “Two Weeks Notice” and Kyra Sedgewick’s in “Labor Pains.”

“I’m cast as an old guy,” he said. “It’s like, ‘Hey, come on, I want to kiss the girls.’ You grow old, but your head doesn’t necessarily change.”

What also hasn’t changed is the legacy he’s created in the world of comedy.

Moving on from his start at Second City in Chicago, he was the first comedian to appear in a live concert on HBO. He went on to do nine, one-man shows for HBO, his most recent – “Robert Klein: Unfair and Unbalanced” – in 2010.

It was a career he set out to achieve in the fall of 1963. Kennedy had been shot. He’d left Yale Drama School and was depressed, staying at his parent’s apartment in the Bronx.

“I’m a failure,” he thought at the time.

He substitute taught for a bit before landing Second City. It’s a story he tells in his book, “The Amorous Busboy of Decatur Avenue,” which ends when he’s 25 years old.

“I learned more at Second City getting $150 a week than I did with my father paying an expensive tuition at Yale,” he said.

The rest of his life story likely will end up in a documentary being negotiated now. A possible name: “I Can’t Stop My Leg,” after the lyric to his most famous comedy song, Klein said.

Music remains part of his act today, he said, with his longtime colleague Bob Stein joining him on stage at the Raue.

“I guarantee fun and a wonderful evening. I don’t stand at a mic and not move. I don’t sit on a stool. I take the stage and patrol it like a wild cat. I’m experienced, and I’m better than I ever was.”