"O" is Buster Witwicky's best friend. If you thought life would be pretty sweet as the hefty white-fro'ed hanger-on of the school nerd and his implausibly gorgeous suckface device, you'd be wrong. No, he's the universe's chew toy. It's not the Twinkies that have made him swell, it's the bitterness.
He is the son of Mister "O".
Marvel Comics continuity
Buster and his girlfriend Jesse were sitting in the former's car at a drive-in theater, making out. "O" was in the back seat, popcorn in hand, wishing they'd quit it (right in front of him, no less), so he could see the movie. A driverless Volkswagen Beetle hit their car from behind, so his friend left the car to check it out.
Fighter jets began attacking the drive-in theater. Buster was suddenly interested in the damaged Beetle, so Jesse and "O" went to get help.
As Buster began to get entangled in the war of the alien robots who called themselves Transformers, "O"'s new job was to stand beside Jesse, who would weep in awe at him from afar, hoping he will be all right, and if only she could be there beside him.
When Buster's father had a heart attack and was hospitalized, "O" and Jesse visited Buster to cheer him up and offer support. Though Buster was a bookworm, he had recently developed a sudden aptitude for fixing cars. Jesse, helping quell Buster's worries that his father's auto repair business would fail in his absence, suggested that since Buster's so smart, he should be able to learn how to fix cars in a few days. "O" grunted a "Yeah, sure."
Buster exploded at the two, pointed his finger at "O," accused him of not appreciating how difficult his father's work is, and told them both to leave him the Hell alone. "O" and Jesse left.
"O" was never seen again.
He is probably much happier now.