Garrison "Gary" Heffley, more commonly referred to as Uncle Gary, is the uncle of Greg, Rodrick and Manny and the brother of Frank and Joe. Not much is known about him, apart from the fact that he was mentioned in book 3, and Greg had to go to his wedding in book 5. He appears as a supporting character in The Third Wheel. He appears in a flashback of Double Down.
Most of Gary's personality is not hinted in the book, but he is shown to be a money-loving person as he always uses up his money to buy Scratch Cards, which he hopes to win. He also appears to fail or leave every job he had in sometime only. He has been shown to be good in relationships with women, having married four times but divorcing every single time, mostly even before the honeymoon.
In The Last Straw
In The Last Straw, Greg mentions that he got a shirt on his first wedding and if he doesn't gets clean clothes he will have to wear it.
In The Ugly Truth
He is heavily featured in The Ugly Truth, as he is getting married for the fourth time to a woman named Sonja. But at their wedding, his best man Leonard stands up and gives a toast that when Gary and Sonja were watching a baseball game while they were dating. Gary thought of breaking up with her and start dating her sister instead, but before he could do that a plane flew with a banner saying "Marry Me Sonja?" Sonja reacted to it thinking it was from Gary, but Leonard said there must've been some other guy with a girlfriend named Sonja but Gary was afraid the guys around his seat would beat him if he lets Sonja down. After hearing this, Sonja got angry with Gary might have divorced her because she isn't seen with him in Third Wheel, so they have possibly divorced.
In The Third Wheel
In 'The Third Wheel' Gary moves in with Greg after borrowing his brother's money to buy a Boston souvenir stand. When Frank sends the money, Gary buys the business before realizing that Boston is misspelled as Botson on the shirts, but he didn't want give up selling them. he also sold one to Rodrick for three bucks, he also keeps on buying scratch cards with the money he gets. Gary gives Greg advice of how to get a partner for the dance and he even gets signed up as a "DJ" at the dance. At Greg's dance, Gary sells the T-Shirts in the dark Paris-Themed room. When the elderly turned on the lights, kids started complaining that they were being ripped off, but Gary distracted them by increasing the music's volume. He then bought a bunch of Scratch Cards, and one of them won him $40,000 so he paid Frank the money he owed him, wished Greg luck in his love life and moved out of the house.
In Double Down
In 'Double Down' Uncle Gary cuts down a big branch that was hanging over his driveway and end up breaking his collarbone