In most incarnations of the series, Scooby is regarded as a unique Great Dane dog who is able to speak in broken English, and usually puts the letter "R" in front of words and noises made. Other incarnations, such as A Pup Named Scooby-Doo, present talking dogs as quite common. In one Scooby series, Scooby-Doo! Mystery Incorporated, Scooby is able to speak in more complete sentences, partially retaining his speech impediment.
Different iterations of the character have been developed and expanded in the various series featuring the characters, many of them contradicting, such as the original series and recent live-action movies where Shaggy and Scooby first meet as older teenagers for the first time, contradicting the A Pup Named Scooby-Doo animated series where they know each other from almost infancy.
In all versions of the character, Scooby and Shaggy share several personality traits, mostly being cowardly and perpetually hungry. But their friends (Velma, Daphne and Fred) encourage them to go after the costumed villains, usually with "Scooby Snacks", a biscuit-like dog treat or cookie snack (usually shaped like a bone or, in later versions of the cartoons, Scooby's dog tag), though Scooby's inherent loyalty and courage does often force him to take a more heroic stance. Scooby is also extremely ticklish and this is seen in many of the television shows and movies.
Scooby has a speech impediment and tends to pronounce most words as if they begin with an "R", though most characters are able to understand him perfectly. In most iterations, he keeps his sentences relatively short, usually using charades for anything longer than three or four words. His catchphrase, usually howled at the end of every production, is "Scooby-Dooby-Doo!" or "Rooby-Rooby-Roo". Scooby was voiced by Don Messick through Arabian Nights in 1994, after which point Messick quit smoking; quitting smoking changed his voice and prevented him from achieving the same raspy vocal effect (despite Messick's efforts, he suffered a career-ending stroke in 1996 and died in 1997, before any further Scooby-Doo productions were made). Messick is also known for providing the voice of the dogs Astro on The Jetsons and Muttley (who snickered).[6] The characteristic voices of Scooby and Astro are so similar that Astro's signature phrase, "Ruh-roh!", is popularly and improperly attributed to Scooby (as in "Ruh-roh, Raggy!").