Actor Paul Reubens was not invited to be a guest on "The Tonight Show" with host Johnny Carson due to Carson's character rule, which prevents him from appearing on the show as a guest. The book "Love Johnny Carson," written by Mark Malkoff, reveals that Carson only made exceptions for guests who were in character, citing Super Dave Osborne (Bob Einstein) or Father Guido Sarducci (Don Novello) as examples of exceptions. While never invited to appear on the “Tonight Show” with Carson in the hosting chair, Reuben did appear in an episode while Joan Rivers served as a special guest host. Many celebrities were banned from appearing as guests during Carson's tenure as host, including Ellen DeGeneres, Jay Leno, William Shatner and others.