From The TV IV
Scooby-Doo is the canine star of the long-running cartoons bearing his name. As a Great Dane, his size should be intimidating but by essence he's a coward. His courage will show up once in awhile, usually for his favorite treat, Scooby Snacks. He is best friends with Shaggy.
Up to 1988, not much was known about Scooby's origins. In the special Scooby Goes Hollywood, he is adopted by the gang at a pet store. Yet in A Pup Named Scooby-Doo, he is what the title says--a gangly pup, owned by Shaggy. (Scooby's birthname--"Scoobert"--is also disclosed, much to his chagrin.) His family has been shown in several episodes since 1976--his goofy cousin Scooby-Dum, movie star Scooby-Dee, parents Mumsy and Dada Doo, circus clown Dipsy Doo, and his much villified little nephew Scrappy-Doo.
Scooby was not the first cartoon character with that name. In 1967, Tom and Tubb's seal friend on Moby Dick and the Mighty Mightor also bore the name Scooby. The "Doo" was tacked onto the canine character two years later after Fred Silverman heard the "scooby-dooby-doo" ending tag of the Frank Sinatra song "Strangers In The Night."
Scooby-Doo was originally planned as a sheepdog named Too Much. He was changed to a Great Dane after the staff recalled that The Archie Show already had a sheepdog named Hot Dog.