Hanna-Barbara and its successor, Warner Bros. Animation, have produced numerous follow-up and spin-off animated series and several related works, including television specials and telefilms, a line of direct-to-video films, and two Warner Bros.–produced theatrical feature films. Although the format of the show and the cast (and ages) of characters have varied significantly over the years, the most familiar versions of the show feature a talking dog named Scooby-Doo and four teenage mystery solvers: Fred "Freddie" Jones, Daphne Blake, Velma Dinkley and Norville "Shaggy" Rogers. Shaggy’s voice is provided by Top 40 DJ Casey Kasem. Scooby’s speech patterns closely resembled an earlier cartoon dog, Astro from The Jetsons .