According to Greg, Rowley is more of a forced friend because Greg always says how Rowley is stupid, idotic, and
childish and why Greg doesn't wants to be friends with him, it was later revealed that when Rowley moved into the neighborhood, he knocked at Greg's door and when Greg opened it, without even introducing himself or saying Hi he started saying jokes from a book his mother bought him,Greg felt a little bad for Rowley and forced himself to befriend him. Greg also shows how much Rowley's parents are overprotective of him. Greg treats Rowley more of a slave by making him do all his work, carry his bag and give him piggy rides, be his campaign manager and when Rowley become the social chairperson in the Third Wheel,Greg thinks that he will boss over Rowley and tell him what to do.However in the movie Greg doesn't seems to do things like that to Rowley, treating him more of a best friend, but still keeps giving his advices to Rowley. Rowley and Greg's relationship is quite strained as they keep fighting and breaking up,then after a while they recouncile their friendship.The First time Greg met Rowley, Rowley didn't introduce himself and started his joke with "Knock Knock" Greg greeted and asked him what he was saying, but Rowley just said "Thermos!" looking at his book, then Greg asked him again what is he doing, Rowley just replied "Thermos Be some funny way to tickle your funny bone!".
Greg has a very bad relationship with Rodrick because they keep fighting with each other and telling on each other. In Rodrick Rules, Greg had a very embarrasing secret, which was of him accidentally going into the ladies bathroom of Leisure Tower. Rodrick throughout the book kept on threatening Greg that he will spill it out if he provokes him or tells on him. Rodrick also threatens Greg to kill him and Greg also fears him and whenever Rodrick sees Greg in his room, he starts chasing him. Rodrick seemed to know that Greg had a crush on Holly Hills in The Last Straw because when they were in a hotel room, Rodrick lied to Greg by saying the Hills family is staying in a room next to their's, Greg fell for it and Rodrick pushed him out of the door and locked the door, Greg was also in his underwear making it worse for him. Rodrick and Greg are rarely seen getting together, however at the end of the Rodrick Rules film, Greg and Rodrick bond and end up etting along with each other.In The Third Wheel Rodrick is a background character and doesn't plays and prank or bothers Greg,making it one the few times for this to happen.
Greg hates his younger brother, Manny alot because his parents always treat him like a prince and would give him everything he wants and when Greg and Rodrick where his age, the parents were more strict with them. His parents seem to spoil him too as they are never seen scolding him even once, in Cabin Fever,he killed all lights except for the one for his room throught electric panel, while his family were struggling, he was enjoying himself until Greg found that, his parents didn't scold him. He also seems to say lies and get away with it like when Greg was playing with Manny in new-years eve and found a little piece of thread and told Manny its a spider and he started pretending if he was making him eat it,just then, Manny slapped Greg's hands and the thread went inside Manny's mouth and he swallowed it too and he told his Mother,Greg told Susan everything, Susan got some small objects in front of Manny and told him to tell which one of them was the closest in size to the thing he ate, Manny got a orange from the freezer,Susan got steamed and sent Greg early to bed.In The Third Wheel he made up alot of Imaginary friends called Joey, Petey, Johnny Cheddar,Charles Tribble,The Other Charles Tribble and Danny, he would use them to escape uncomfortable situtations, like when he broke a plate,he blamed Johnny Cheddar, Susan thought Manny would get traumatized if she told Manny that his friends are fake and gave his imaginary friend a time-out and the time-out chair was a new re-cliner which Greg liked and he couldn't sit on it.
Robert Jefferson (Rowley's Dad):
Greg and Robert seem to have a very bad history as Robert always thinks Greg is a bad influence for Rowley and he often tells Rowley to stay away from him, Greg describes him as a very protective parent as he doesn't even lets Rowley play a video game with a slightest bit of violence.and won't let Rowley ride scary rides in the boardwalk as seen in Dog Days.
Greg actually doesn't like Susan as she often embarrases Greg by calling him words like "sweetie" "sweetie pie" and "honey bunches".Susan always takes Manny aside and she would not tell Manny that his imaginary friends are fake otherwise she thinks he will be "traumatized", Greg hates how his Mom never punishes Manny and treats him like a prince and spoils him, even though he changed his password on Net Kritterz, changed the parental control and refused to give the password, and cut power in every room except his, in Cabin Fever.
Frank thinks that video-games are just a thing to keep Greg away from excersising and he would make Greg eat more and work-out and he also threatned him that he will send him to the military academy, Spag Union if he doesn't shape up in The Last Straw, Greg was also steamed after he stole his and Rodrick's snacks from the pantry.
Ben Fielders (Online Book):
Ben Fielders was Greg's old best friend in the online book until he moved away. However he does return and Greg describes about how he and Ben used to have a popular comedy group which many people liked.When he returned, Greg asked him about a girl called Piper Matthews (the online counterpart of Holly Hills)Ben told him untrue things about her, Greg believed him as she was Ben's classmate.When Greg went to the roll-a-round, he saw Piper there, Greg was about to go there and ask her to go with him, but when couples skate came,she an Ben paired up, Greg found that Ben just told the untrue things to keep him away from her and that she is actaully Ben's girlfriend, Greg got mad and reported on Ben about a bad thing he and Ben did at the church school walls to the church.
Greg has no relationships with Holly in the book series,in the Last Straw Greg wanted to impress her because she was according to Greg the only girl in his class which he liked and didn't have a boyfriend.However when Greg went to roll-a-round,she called Greg "Fregley",this made Greg lose interest in her,in the same book Holly wrote in Greg's yearbook and used his real name and said he was OK.Greg was fine with that and started to get interest in her again,but Holly wrote in Rowley's yearbook that he is cute,this disappointed Greg. In the Movie Series though Greg and her may have become a couple at the end of Dog Days (Movie).
In the book Dog Days,Greg had a crush on both Heather and Holly,he thought that if he would get good with Heather he could get a highschool girlfriend (a thing he has been wanting for a longtime) and so he could show off to kids at his school.So then he found that she is a lifeguard at the pool,when they got to the pool Greg would go to the pool which she is lifeguarding on,and Greg would excersise in the bathroom so he could have his muscles pop up.Greg thought to impress her he would say anything to a kid doing anything bad (which Heather was supposed to say).Once a kid was feeling bad and he vommited,Heather went to clean it and asked Greg to help her clean it,but Greg just ignored her because he was scared of cleaning the vomit.Soon Greg thought that Heather will soon go to college and that long-time relationships won't work. in the.In the Dog Days movie,Greg doesn't has a crush on her,but in the credits he appears trying to show his muscles to her and her friend.
According to Greg,his uncle Charlie brings everything for him on christmas. However when he asked for a barbie dream house (thinking it would be a great fort for his toy soldiers),Charlie went and bought the first thing which had barbie in it,this caused Greg to get a barbie doll. And when Greg asked him from twisted wizard,he got a photo of himself about the same size as the box of Twisted Wizard. When Greg was little,he used to call him "red" which was because Greg had Red Pajamas,however Greg took it seriousley. He told his mother about it,and she bought him Blue ones,but Charlie gave him a nickname "blue".
Arthur Heffley/Clyde Heffley:
Arthur is the great-uncle of Greg and only says "Muurp" "Ruup" instead of words,making Greg confused if he is actually meaning something or not. So Greg just takes a response that would be suitable like "No Thank You" and more. In the online version,there is a great-uncle of Greg called Clyde Heffley who has a different appearance but plays the same role but appears at the Heffley's house at thanksgiving day and stayed there for two days.
Greg finds Fregley weird and creepy.Whenever Greg is going to Rowley's house,he always sees Fregley in his backyard,saying creepy things,this causes Greg to go through by going in the gutters.When Rowley broke up with Greg and was hanging out with Collin Lee (his backup friend),Greg thought of making him jealous by having sleepover at Fregley's.When he went there,he would stay away from Fregley as far as possible.Fregley then apologized to him for chasing him with a booger.In the film,Fregley chases him with a booger instead.
Chirag is sort of Greg's friend, as Greg and Chirag are always playing practical jokes on each other (e.g. Invisible Chirag) but they still get along well. Chirag moves to India in a few books, but he comes back. Chirag, according to Greg, is extremely short and Greg only picks on him sometimes because he's the only person he can pick on, as he's so short. Apparently, Chirag was the smallest kid in the school in 6th grade.
Greg knew Dean Delarosa when he was in the third grade and was invited to his birthday part, but his mother got the date wrong by a week and Greg ended up coming a week early.Greg liked the gift he was supossed to give him, that he ended up playing with it.Dean was Greg's secret holiday buddy when the kids had give each other presents anonymously, Greg forgot, but Susan got it and gave it to Greg and Susan didn't knew that it was supposed to be anonymous so Greg and Dean felt embarrassed when the teacher called out Dean's gift's label.