Jack E. Leonard was an American comedian whose sarcastic insult-based humor was imitated by Don Rickles.Born Leonard Lebitsky on April 24, 1910, Leonard made his show business bones as a nightclub comedian and became well-known to the public for his appearances on TV variety and game show after breaking through on Tonight Starring Jack Paar (1957).In addition to his night club act and TV gigs, he made comedy records. On the night of May 9, 1973, Leonard suffered a heart attack and collapsed just after coming off-stage at a performance at the Rainbow Room at New York's Rockefeller Center. He died in hospital early the following morning after undergoing cardiac bypass surgery. He was 63 years old.