Jonathan Katz is an American comedian, actor, and voice actor who is best known for his starring role in the animated sitcom Dr. Katz, Professional Therapist. He currently hosts a talk radio show titled You're on the Air with Jonathan Katz.

Dr. Katz originally aired on Comedy Central from 1995 to 2000, and starred Katz as a professional therapist whose patients chiefly comprised of other comedians and actors. He received an Emmy award for his work on the show in 1995 for Outstanding Voice-Over Performance. His voice can also be heard in the animated series, Home Movies, a show with many ties to Dr. Katz.

In 1996, Katz was diagnosed with multiple sclerosis. The initial symptoms began in 1996: "I was working on a TV show called Ink with Ted Danson, and after every episode we would take a curtain call and I noticed that I needed a head-start." Over time, he found it difficult to hide his physical condition behind his jokes: "I was producing a show, and it was too physical a job for me to get from one location to another and I had to pretend I could keep up with everybody. My manager and attorney said, 'In Hollywood you can't be old or sick.' "

But hiding his condition became too much of a burden for Katz, and he eventually disclosed it. Now he speaks publicly as part of a tour sponsored by a manufacturer of medications used to treat MS: "People have been pretty supportive; nobody never had me in mind for an action film because of the kind of work I do -- mostly in the world of animation, which is not a big issue because as a person, I can't run that fast; as a cartoon character, I can fly -- literally." Katz, who now gets around with the help of a motorized scooter, says he doesn't regret his decision: "One of the reasons I disclosed my condition is because it is much easier to live with MS than to pretend you don't have it. If I could convince everyone of that, my job here is done."

Originally a musician and songwriter, Katz fronted a rhythm and blues group called "Katz and Jammers" before serving as the musical director for Robin Williams' 1979 stand-up tour.

He was the New York State Ping Pong champion in 1964.

He is a close personal friend of renowned playwright David Mamet. They used to travel around college to college hustling people over games of ping pong. Katz would let Mamet beat him. They would pretend to play for money then Mamet would say "If you want to play me, you have to beat my friend first." To keep the game moderately close, he would sometimes spot his opponents 15 points for a game up to 21 and during every point, recall a painful experience from his childhood.