 Episodes often feature guest voices from a wide range of professions , including actors , athletes , authors , bands , musicians , and scientists . Many guest voices star as themselves . Leslie Uggams was the first to appear as herself , in the fourth episode of the first season , " Mind Over Murder " . The episode " Not All Dogs Go to Heaven " guest starred the entire cast of Star Trek : The Next Generation , including Patrick Stewart , Jonathan Frakes , Brent Spiner , LeVar Burton , Gates McFadden , Michael Dorn , Wil Wheaton , Marina Sirtis , and even Denise Crosby ( season 1 as Tasha Yar ) , playing themselves ; this is the episode with the most guest stars of the seventh season . 
