The title character is The Great Grape Ape (voiced by Bob Holt), who is a 40-foot purple gorilla with the mind of a child. His catch phrase is saying his name twice ("Grape Ape, Grape Ape") after anything anyone says, usually as a form of agreement or acknowledgement of what was said. He travels the countryside with his canine pal Beegle Beagle (voiced by Marty Ingels), whom he calls "Beegly Beagly".
Grape Ape's immense size tends to initially shock and frighten those unfamiliar with him, and his presence alone has often terrified people and animals, causing them to run off screaming invariably: "YEOW! A gorill-ill-ill-ill-la!". The only exception to this was the character Rosie O'Lady (voiced by Janet Waldo), who appeared in Episode 11, "The Indian Grape Call". When asked by Beagle why she did not yell in fear like everyone else did upon seeing Grape Ape, she simply said, "You've seen one 40-foot purple ape, you've seen them all". In "Ali Beagle and the Forty Grapes", a wooden city limits sign reacted to Grape Ape's presence (after "overhearing" that no one else had) by progressively displaying the "YEOW!" phrase, with Beegle reading aloud as the sign changed, unfolding additional segments for the several "ill[a]" syllables (after which it folded itself up and hopped away in fear).
Grape Ape and his friend Beegle Beagle usually ride around in a small yellow van driven by Beegle Beagle with Grape Ape sitting on the roof which can somehow support his weight. A recurring bit of business would be for him to "rev up" the tiny vehicle like a child with a friction toy, then hop aboard as the van would start on its way. Also, Grape Ape's steps would often bounce Beegle into the air, where his legs would keep walking without breaking stride.