Simplify the following text for a Grade 4 native English-speaking person.
Original: Occasionally , between 1982 and 2001 , Zevon filled in for Paul Shaffer as bandleader on Late Night with David Letterman and later Late Show with David Letterman .
Simplified: He was often a guest on Late Night with David Letterman and the Late Show with David Letterman . Letterman later sang with Zevon on `` Hit Somebody !