Penn Zero obtained the job as part-time hero when his parents, Brock and Vonnie Zero, found themselves trapped in the "Most Dangerous World Imaginable", with no way to escape but enough experience to stay alive. From then on, he lived with his Aunt Rose and Uncle Chuck, and could communicate with his parents via the Multi Universe Hologram Uplink (MUHU). As a part-time hero working for Phyllis, he is joined by his best school friends Boone and Sashi to hop through dimensions using the Multi Universe Transprojector to foil the plans of his art teacher Rippen and the Principal Larry.
Calling her the smartest and toughest of girls, Penn appreciates Sashi's friendship and assistance. He relies on Sashi heavily when it comes to pulling off complicated tasks like retrieving the magic sword and escaping the prison cage in "North Pole Down". Whenever Sashi's being more aggressive, Penn is terrified by her, like when she wasn't pleased with his trick in dodgeball in "3 Big Problems", but at other times he enjoys making fun of her like when she gets a silly form or he's not fazed by it. He calls her out for being so violent, stubborn, and a bit crazy in "The Princess Most Fair", but when she admits she feels left out of Penn and Boone's close bond, he reassures her that she is the glue to the group, keeping the team on the rails.
His best friend.
In Rip-Penn, Penn loses his temper larry taking about pinwheel story.
- Penn sleeps with a teddy bear, as revealed in "The Princess Most Fair".
- In "The Old Old West", Penn is shown to be able to fix his scooter while talking to his parents.
- In "I'm Super!", Penn reveals that he had always wanted to be a superhero since he was six years old.
- It's revealed that in "The Ripple Effect", his family has never failed a single mission, hence why their last name is Zero.
- As shown in "Rip-Penn", whenever he loses his patience, he loses his temper as well.
- Also in the same episode, it's revealed that he is afraid of sock puppets and dying (with the latter being developed after nearly dying in "Totally Into Your Body").
- In Lady Starblaster revealed that Penn is a talented dancer.
- In "Zap One", it's revealed that he initially wore a blue-green sweater before he had his trademark shirt and fake chain mail mesh, which were gifts that he found from his parents after his first mission. Moreover, his MUHU was also a gift from them.