Dr. Brainstorm built Jack originally to be his robot slave, who would do anything and everything he told him to do. Unfortunately, this is not what he got. Jack is a shiny, silver robot, about as tall as Calvin's parents. Whenever he's in Brainstorm's lab, he's always reflecting whatever he's standing in front of. He has a round head with bolts and screws on the top, and a long pointed silver nose. His legs are segmented so that he can extend them outward, and take long strides. He never uses this feature though. His feet are simply metal rounded blocks. He has arms and five fingers on each hand just like any human. Jack never takes Brainstorm seriously. Always calling him by his dreaded first name, Jack is more of a good guy than a bad one. He does nothing to help Brainstorm whatsoever, and yet Always helps Calvin and Hobbes when they're in trouble Or whenever he feels like it. Whenever he's not walking or sitting, he leans against whatever's handy. He's always being sarcastic at everyone, especially Brainstorm, and whenever he's not reading his Robots Weekly magazine sipping milkshakes or sodas, or being forced to come along on Brainstorm's lunatic missions, he watches with entertainment, as Brainstorm makes pathetic attempts to take over the world. He is voiced by Mark Hoppus.
- He hates child actors.
|Main Characters||Calvin • Hobbes • Susie Derkins • Calvin's mother • Calvin's father • Miss Wormwood • Andy • Socrates • Sherman • Moe • Dr. Brainstorm • Jack • Iron Calvin • Zoe • MTM|
|Secondary Characters||Principal Spittle • Galaxoid • Nebular • Mr. Bun • Spaceman Spiff • Stupendous Man • Tracer Bullet • Simon • Carol Derkins • Dark Calvin • Avery • Albert • Tyler Roseman • Magical Tiger • Rupert • Earl • Nivlac • Sebboh • Safari Al • Snow Goons • Dave|
|Minor Characters||Warry • Dopey Alien • Sally • Athlea • Future Counterparts • Dilophos • Derek • Mr. Johnson • Henry • JadaLeininger727 • Burnt Out Star • Dark Calvin's Demons • George • Tiger Eye|