#1 Don Messick
The original voice who first gave life to Scooby Doo belongs to Don Messick. He was a well-known and legendary voice actor for his performances in the Hannah Barbacena Cartoons.
He had voiced the title character in all of its appearances since 1969 until he outed the role in 1996.
He then died in the year 1997.
#2 Casey Kasem
Casey Kasem was a disc jockey, actor, and radio personality who first provided the voice for Scooby Doo’s sidekick, Shaggy, from 1969 until 1997.
He was also known for hosting countdowns such as the famous America’s Top 40.
By 2002, Kasem reprised his voice role as Shaggy up until 2009.
He then retired from hosting countdowns as well as his career in voiceovers in the same year (2009).
In 2013, it was revelead that he had Parkinson’s disease.
Kasem died on June 15th, 2014, from Lewy body dementia.
#3 Franklin Wendell “Frank” Welker
Fred Jones was voiced by Frank Weler. He is an actor, voice actor, impressionist, and a former stand-up comedian.
He has been the only voice actor who has voiced Fred Jones since 1969 up until now.
In 2002, he took over the role as Scooby Doo’s voice actor, and he has been voicing the character up until now.
#4 Stefanianna Christopherson
Stefanianna Christopherson is the original voice of one of the human protagonists in Scooby Doo, Daphne Blake.
According to IMDb, she was an actress, known for Scooby Doo: Where Are You! (1969), Scooby Doo’s Spookiest Tales VHS (2001) and Star Crystal (1986). Also, she was previously married to Rabindra Danks. She had voiced Daphne since 1969 until she left after married in 1970.
As of now, there are no updates about Stefanianna Christopherson.
#5 Nicole Jaffe
Velma DInkley was voiced by Nicole Jaffe.
According to IMDb, her career is mostly based on voice-over work.
After the New Scooby Doo Movie ended, she left the Hannah Barbacena Studio and became an agent for actors and actresses at the William Morris Agency in 1974. In 2003, she reprised the role for the retro-styled DTVs Scooby Doo! and The Legend of the Vampire and Scooby-doo!, and the Monster of Mexico.
As of now, there is no new information about Nicole Jaffe.
However, as stated on IMDb, she is still working as an agent at the same company since 1974.