Bill (voiced by Charles Adler) is Scooter's whiny, ill-tempered partner in the invention game. He gets to test drive the newest devices often with ill, chaotic and disastrous consequences. When he's intact from a failed experiment, Bill must watch out for a dangerous species of Jungle Slug who likes to eat him. A jungle slug once succeeded in eating part of his brain, or as Scooter dismissed it "just a tiny part of your mind". Throughout the series, he is known for his catch phrase "When does the hurting stop?". Bill is continually depressed, sometimes almost to the point of psychosis. He appears to have a deep-seated hatred for Scooter, having even tried to kill Scooter with a rock while muttering his catch phrase.
Scooter (voiced by Curtis Armstrong) is a jolly, overly enthusiastic caveman and is blissfully unaware of Bill's attitude toward him. He loves to invent such things as a square wheel, baseball (actually "beesball" because they use a beehive as the ball), a washing machine that uses fire, and the pogo stick. Predictably, his inventions often have disastrous consequences for which Bill is the victim. Although Scooter's inventions would fail; sometimes his inventions would save him and Bill from being hurt by the Thunder Lizards, such as when he invented Groucho glasses and a smart bomb failed to detonate on account of the joke glasses disguising their faces. Another episode had a UFO land and an advanced race called the "Goalings" introduce themselves to Scooter and Bill. When they left their three-holed sphere (which contained the key to world peace and harmony) with the humans, Scooter used it for a game to knock over pins and called it "Goaling" in honor of the aliens. Bill actually commented Scooter finally invented something that is beneficial.