Billy Rotner is a friend of Rodrick and a member of community service.
He did community service for stealing a pack of gummy worms from a convenience store. His excuse for his actions goes back to when he was a kid. He claimed that his mom once bought him and his brother a pack of gummy worms to share, but his brother ended up eating them all. Then he states that the only reason he stole that packet was so he could finally have some gummy worms for himself.
When Greg attempted to escape the tyrannical eyes of the girl scouts during the park cleanup, Billy and Frew follow him. And when Greg tells him to go back, Billy says that he is through with community service and is NEVER going back.
Greg turns around to go back himself, but all of the sudden a Brownie steps out of nowhere and sees them. All three of them begin to run, but the next thing they know, the entire Girl Scouts troop is in hot pursuit. Eventually Billy takes the lead, and the rest just follow him. Greg noticed that Billy seemed to know what he was doing, so he guessed that he probably had experience with that sort of thing.
When they think that they've finally lost the girl scouts, they stop to catch their breath. Billy pulls a few rolls of Thin Mints that he had in his jumpsuit, and divides them up between him, Greg, and Frew. Greg suspected that Billy never even payed for the cookies, but never asks.
Then Billy says that they should all ditch their clothes just in case the authorities used dogs to track them. That's when Greg realizes that if Billy couldn't get away with stealing a pack of gummy worms, he's the last person they should be taking advice from. His thoughts were obviously shared by Frew, since he was stripping to his underwear along with Billy.
Greg suggests that they split up, but Frew said they should stick together. He says that they could travel across the country having crazy adventures and maybe even join the circus along the way. Billy liked that idea, but then the two of them started arguing over who would have the right to a movie if they ever became famous.
As soon as Greg gets the idea to slip away, a bunch of vans pull up. The lead van is being driven by Susan Heffley, and the rest are full of Girl Scouts. When Susan demands to know what they were thinking running away, Greg pins the whole thing of Billy, since he figured that he would be going down no matter what. Billy probably got more community service tacked on to his sentence for what he did.
Later in the book, Greg is stranded on the highway while Grandpa goes for gas. As Greg is waiting, he sees a bunch of people walking towards the car on the side of the road. He gets scared when he sees their orange jumpsuits (signifying that they are members of community service) and when he sees that one of them is Billy Rotner, he hides below the car's dashboard. But instead of passing the car, the community service guys hang around it for their lunch break. When they finally leave, they leave a huge mess, but at least then Greg could come out of hiding.
- Diary of a Wimpy Kid: Old School (First and only appearance)