Callum is a bit short for his age, being around 5'6" and not likely to grow any more. He doesn't usually get comments on this, mostly because people don't talk to him a lot, but he doesn't mind it either way. He has muddy green eyes and short brown hair. Spending a good amount of his time on his laptop or desktop computer, he isn't fit, but he isn't chubby either; he tries to keep a healthy diet but usually ends up eating less than a healthy amount of food because of his hyperfiscation on work.

Callum is a usually shy and quiet individual. It's a wonder he even has friends at all, though many of those he considers "friends" are really just coworkers who ackwardly avoid his eye contact at the water dispenser or random strangers he's stuck talking to at bars (via association with Oscar.) He's actually quite a bookworm, though he spends much of his time working or obsessing over work, so he doesn't actually get to read that much. He takes his work very seriously; as a workaholic, he works in a firm and at home. Since he lives alone in his apartment, there isn't much of anyone to stop him.