Johnny Carson's strict character rule kept Pee-Wee Herman from appearing on 'Tonight Show': book

Actor Paul Reubens never got the opportunity to sit across from Johnny Carson as a guest on "The Tonight Show," and "always wondered why."

According to the book, "Love Johnny Carson," written by Mark Malkoff, the actor, known for playing the iconic character, Pee-Wee Herman, was not invited to be a guest on the show with Carson in the hosting seat because at the time, "Reubens was only going on shows ‘in character’ as Pee-Wee."

"Carson wouldn’t put on guests that were 'in character' if he thought the home audience might be confused if they were real or not," Malkoff wrote. "It was the same reason Carson refused to book Gilbert Gottfried or Bobcat Goldthwait."

The author explained that Carson only made exceptions for people when "it was plainly obvious that it was a 'put on,'" citing Super Dave Osborne (Bob Einstein) or Father Guido Sarducci (Don Novello) as examples of exceptions to Carson's rule.

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Malkoff wrote that Carson's rule was in effect from the beginning of his show, noting he "was convinced that first time guest Bob Uecker" was a guest on his show in 1969, that he was a "comedian 'pretending' to be a former Major League baseball player" and that a staff member had to show him newspaper articles to prove he wasn't pretending.

"Carson’s biggest question if a guest was real or going on in character was singer Tiny Tim who debuted in 1968. Carson by the end of Tiny’s debut on ‘Tonight’ figured out that Tiny was genuine. The next year in 1969 Tiny Tim got married to Miss Vicki on Carson’s Tonight resulting in 40 million viewers tuning in."

While Reubens was never a guest on the "Tonight Show" with Carson in the hosting chair, he did appear in an episode while Joan Rivers served as a guest host.

In 1985, Reubens was a guest on the "Tonight Show" for a Halloween episode while Rivers guest hosted in place of Carson. Reubens also appeared as the first guest on Rivers' late-night talk show two years later, with Malkoff writing, "Pee-Wee appealed more to Rivers’ younger, hipper audience," while Carson's older viewership might not have appreciated that kind of humor.

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A number of celebrities have found themselves on the infamous "Tonight Show" ban list.

According to Malkoff, many big celebrities were barred from appearing as a guest during his tenure as the show's host, including Ellen DeGeneres, Jay Leno, William Shatner and others.

Leno, appeared on the show a number of times before getting banned. A decision which came after his fifth appearance in February 1978, when "the audience laughs were so light that Johnny decided never to invite him back," according to Malkoff's book.

"Tonight Show" stand-up talent scout Jim McCawley wrote in his unpublished book that producers were told by Carson not to invite Leno back. Malkoff wrote that McCawley tried to fight for Leno, but producer Peter Lassally shut him down.

"'Johnny just doesn’t like him. He doesn’t like his jokes,' said Peter," Malkoff wrote. "That’s not going to change… Once he doesn’t like someone, he doesn’t start liking them later."

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Leno eventually returned to the show, later going on to host "The Tonight Show" for a combined 22 years, first from 1992 to 2009 and then from 2010 to 2014.