In the early days of Williams Street, many characters were recycled for use in their shows from different Hanna-Barbera productions, this practice fell out of use after Aqua Teen Hunger Force.
Birdgirl (Judy Ken Sebben)
Birdman and the Galaxy Trio "Birdman meets Birdgirl" (1967)
Harvey Birdman
Birdman and the Galaxy Trio "X the Eliminator" (1967)
Black Widow
Space Ghost "The Web" (1966)
Brago
Space Ghost "Brago" (1966)
Brak
Space Ghost "The Lure" (1966)
Creature King
Space Ghost "Creature King" (1966)
Cyclo
Space Ghost "The Cyclopeds" (1966)
Dr. Nightmare
Space Ghost "Nightmare Planet" (1966)
Dr. Soonev
Space Ghost "The Energy Monster" (1966)
Jan
Space Ghost "The Heat Thing" (1966)
The Lizard Slavers
Space Ghost "The Lizard Slavers" (1966)
Lurker
Space Ghost "Space Sargasso" (1966)
Mentok the Mind Taker
Birdman and the Galaxy Trio "Mentor the Mind Taker" (1967)
Metallus
Space Ghost "Homing Device" (1966)
Judge Hiram Mightor
Moby Dick and Mighty Mightor "The Monster Keeper" (1967)
The Mind Taker
Space Ghost "Jungle Planet" (1966)
The Moss Men
Dino Boy in the Lost Valley "The Moss Men" (1966)
Moltar
Space Ghost "The Ovens of Moltor" (1966)
Parko/Owlie
Space Ghost "Space Birds" (1966)
Scooby
Moby Dick and Mighty Mightor "The Sinister Sea Saucher" (1967)
Phil Ken Sebben
Birdman and the Galaxy Trio "X the Eliminator" (1967)
Sisto
Space Ghost "The Lure" (1966)
The Sorcerer
Space Ghost "The Sorcerer" (1966)
Tarantapod
Space Ghost "The Web" (1966)
Zorak
Space Ghost "Zorak" (1966)