Greg had the user name of XxVoid_CowboyxX on PHO, where he was guarded with his identity. He received several bans and probations while on the forum website, including a notable one for lying about being in the city after the aftermath of Leviathan.
Greg Veder was a class mate of Taylor's from Winslow High and was one of the few who actually interacted with her. He is noted as being one of the few to make several attempts to speak to Taylor in the story.
↑In the social sense, Greg is like a car with bald tires. No brakes, skids like hell. He takes a topic, he runs with it, and faced with an obstacle or problem he takes far too long to 'get it' and actually stop or change direction, even after other people would've just realized they can't or shouldn't move forward.
In relationships with people, with things like Parahumans Online, he makes assumptions and runs with them. This combined with his social sense means that he tends to push and situate himself uncomfortably when it comes to boundaries and rules. Forum rules with PHO, school rules, social groups and class teamwork.
He's super passionate about things, and throws himself into them headlong, again with bald tires. He has a game he likes and he puts fifty to a hundred hours into it in the course of a week. Can be a movie, tv show. Unable to muster the right language to convey why he's so passionate about these things, he just doubles down. In short, there's no quality to what he's saying, only quantity, and in delivering that quantity, he pulls from stuff he's read and videos he's watched and other things from his obsessive following of the FotM passion and doesn't convey a consistent narrative. Verbal diarrhea.
A good way to represent Greg's emotional landscape would be to double his emotions. He's not just excited, he's double excited - vibrating with anticipation. He's not just upset, he's double upset - he's crestfallen, destroyed. It's not that he's actually experiencing double the emotion, it's just that the filters and barriers aren't there. He never learned how to hold back or express anything but the absoluteness of what he feels and experiences, and he likes to experience things absolutely.
In taking all of these things, applying them to non-cape life, I would say that he's the type to fall in love a little with any girl he spends more than a few minutes with. He will obsess over cape stuff, but run away with assumptions about how things are or should be, or about what he's dealing with. He believes in labels and celebrates them, often in the sense of being a gamer or otaku. He's emotionally immature, and him finding emotional maturity would be a solid character arc for a story featuring him.
I would gently suggest that making him angry would be the wrong direction, and would point out that he's not actually friends with Sparky, and wouldn't be (well, he'd try, but... no, he wouldn't end up being friends with Sparky). Greg is a puppy given human form. It takes a monumental amount to turn a puppy into something snarling, aggressive, and angry, and in creating that personality, you destroy the puppyness of the puppy. Far more likely to be fearful and retreat/withdraw. - WOG from Wildbow on Greg's personality