- "I've been going to Spag Union Prep School. They really turned me around. You may remember I was a bit of a troublemaker."
- -Lenwood Heath at the public town pool after he finished Spag Union
Lenwood Heath was, according to Greg Heffley, the "baddest teenager" and juneville delinquent in their neighborhood and was described as being the "archenemy" of Greg's dad, Frank Heffley, until after Lenwood's parents sent him the Spag Union Military Academy. Lenwood's first appearance was in Diary of a Wimpy Kid: The Last Straw.
As mentioned above, Lenwood was sent to a military school by his parents as a consequence of his bad behavior, and when he came back home for a brief time, he was spotted by Frank, who was surprised and impressed by Lenwood's change in behavior. In the book, the Heffleys spotted Lenwood working at the mall's movie theater, while the in the movie, Dog Days, which was a mash-up of the third and fourth books, he was seen working as a lifeguard at the city pool. When Greg saw his dad's reaction to Lenwood's change in behavior due to him attending a military school, he got worried that his dad would get the idea to send him to the same military school that Lenwood's parents sent him to.
It's possible that Lenwood may be friends with Rodrick Heffley, or they could at least go to the same school.
According to Greg, Frank had called the police on Lenwood multiple times before Lenwood's parents shipped him off to Spag Union. When the Heffleys ran into Lenwood for the first time after he started attending Spag Union, he had his hair in a buzzcut and looked "like he just graduated from the Air Force." Greg says that the last time he had seen Lenwood before that, he had long hair and was lighting someone's trash on fire (which may have started a minor arson).
In the online version, Lenwood's look is the same except his nose is smaller at the base.