Scoobert "Scooby" Doo is the talking Great Dane pet of the Mystery Inc sleuth team, and star of the massive "Scooby-Doo" franchise. His owner is Shaggy Rogers, both of which are infamous cowards throughout each mystery, and are always hungry for food. Scooby's speech usually involves beginning each word with a "R" sound, developing his signature voice. His trademark catchphrase is of course "Scooby Dooby Doo!", which he often howls at the end of each mystery.
Don Messick originated the voice of Scooby-Doo, and was the voice of the character for over 25 years until his retirement from voice acting in 1996 (he subsequently passed away the following year).
The first replacement voice for Scooby was Hadley Kay, who briefly voiced the character for ads and cameos (notably his Johnny Bravo appearances) until Scott Innes was cast in 1998, and continued the role until 2001 when he was dropped from the role due to location issues (though he still occasionally voices the character in some toys, video games, and other merchandise). Since 2002, Frank Welker (who had originally auditioned for the role when the franchise first began) has been Scooby's voice.
For the two original live-action Scooby-Doo films, Neil Fanning voiced Scooby. For the two recent TV movies, Frank Welker reprised the role from the animated franchise.