Graham Bertran was one of Greg's cabinmates at Hardscrabble Farms during an annual (for one grade in Greg's school) one week trip Greg and his school went on. Little is know about Graham Bertran, because little is said about him. During the ropes obstacle course (Graham and his cabin mates had to get through an obstacle course with ropes tied to each other) when Graham and his cabin mates were struggling at it, Graham is seen falling to the ground, although it is never mentioned in the book, and only seen in an image. During mail call Graham got a big box which he originally mailed to himself before the trip began. When Graham and his group went to their, cabin Graham opened the box when their group's chaperone Mr. Jefferson was gone because the box contained snacks and junk food (that weren't allowed in camp and he didn't want to get himself busted for having those things) mixed in with camping supplies. He shared the content with his group and when Mr. Jefferson returned, the items from the box where hidden under a blanket so Mr. Jefferson wouldn't know about them. Mr. Jefferson never finds out about the items of the box.
He and his cabin mates decided to stage a raid on the girls cabin to steal their deodorant in a desperate attempt to reduce the stink of their cabin. When they got to the cabin Graham helped lift Greg up through an open window into the cabin only for Greg to see the room filled with Girl Scouts, he attempted to call-off the raid but by then it was to late as Graham was already coming through the window wheb he slipped and fell to the floor the sound of which woke everyone up.
- Diary of a Wimpy Kid: Old School (First and only appearance)
- During the ropes obstacle course (an obstacle course that uses ropes tied to each other) Graham falls when him and his cabin mates are struggling on the course, but Graham falling is only seen in an image and never actually mentioned in text or words.