Role in Rodrick Rules
Joe comes to Greg's house late for Thanksgiving. His children all call their uncle "Aunt Fwank (Frank)." Susan says that this is cute but Frank says that Joe taught them to do that. When Frank goes down to the basement to do edits to his Civil War diorama, Joe sneaks down and says "Nice toys, big brother!" Frank explains everything to Joe, but Joe didn't listen to a single thing he was saying. Greg mentions that the year before that book takes place, Manny was approximately 2 weeks from getting out of diapers, but Joe puts a stop to it by saying "Watch out for the 'potty monster,' little fella!" Every-time time Frank had to change a dirty diaper after that, he started cursing Uncle Joe under his breath!
Role in The Last Straw
Joe makes a brief appearance on Easter at church. Greg says that when the songs start, he holds Greg's hands, even though he doesn't have to. Greg also says he has an iron grip. when they sat down Greg makes a cuckoo sigh to show he wasn't part of the holding hands to Holly and the rest behind him.
Role in Dog Days
Role in The Ugly Truth
Uncle Joe is evidently the most troublesome character in the series, who inadvertently embarrasses, annoys and harms Frank by causing him lots of pain and disgust. Uncle Joe is classified as very immature, childish, and overly-affectionate.
Uncle Joe is shown having a Mexican-style mustache, black hair and western-style clothing, looking more like a cowboy in Greg's illustrations. Even though he appears to be designed like a teenager.
- Even though Uncle Joe is younger than Frank, the illustration of his mustache and other features may imply that Uncle Joe is older than what Greg's portrays him to be.
- Uncle Joe is quite possibly the only character to be universally disliked by Greg, Rodrick, Frank and Manny.
- The Ugly Truth is the only book in which Uncle Joe gets along with Frank.
- He does not have a visible mouth in the online version.
- He doesn't appear or mentioned in The Third Wheel, Hard Luck,The Long Haul,Old School, Double Down, and The Getaway. This could mean that his character has been retired.
- In a flashback in Cabin Fever, when Greg snuck into his mother's email account to tell everyone to coordinate all of the Christmas presents will get Greg, Joe's name can be seen.