For the next several years, he worked steadily in Las Vegas, and made hundreds of television appearances on various panel and variety shows.

[4] Leonard's comedic method was sarcastic and aggressive, creating an "insult humor" genre which anticipated Don Rickles.

(Leonard was roastmaster at the Friars' Club roast of Rickles, who he introduced as "a man who's been doing my act for about 12 years now.")

He wore a distinctive outfit: a dark suit, purposely two sizes too small, a white narrow-brimmed hat, and horn-rimmed glasses.

In March 1973, he collapsed shortly after finishing a performance at the Rainbow Room in New York City and underwent emergency cardiac bypass surgery, but died several weeks later at age 63.