Where the hell you been? You have any idea what's goin' on out there?
Tommy was born sometime during the 1980s, in Texas, where he grew up alongside his older brother Joel who raised him. Although not much is known regarding Tommy's early life, the brothers rented two Harley motorcycles and went on a cross-country ride for Tommy's birthday. Through hints between Joel and Tommy's brief conversations in the game, it is likely that they both shared an interest in college football.
Tommy presumably worked alongside his older brother, and regularly went with him and Sarah to several events and carnivals, evidenced by the photos in her room.
Tommy was with Joel for the initial years after the outbreak and aided him in ambushes and raids. It is also very likely that Tommy himself had killed innocent people, as he claims to still suffer nightmares from the years he spent with Joel and all the horrible things they did. Tommy has been seeking redemption for his past crimes by helping Maria build safe havens and communities throughout Wyoming. He cares about those under his charge and puts their well-being before his own.
They're good men. This place gives 'em a second chance. It gives us alla second chance. So, why'd you leave Boston?
Like Joel, Tommy has a short temper, but his is much quicker to diffuse than that of his brother, due to him being generally more sympathetic. His sympathy is shown early on when he tries to stop to help a family during the outbreak but stops when Joel insists they don't; Tommy likely yielding due to a 'big brother knows best' view. Tommy also takes the time to scavenge a photo of Joel and Sarah from what remains of their home, bring especially sympathetic to his brother through such.
Tommy becomes frustrated when Joel brings up his past and blames him for most of it, indicating that Joel may have led a lot of their activities. However, he is surprisingly quick to forgive his brother when they meet again after many years, and despite being more averse to violence, he is capable of violence when he has to be and still loves and cares for his brother Joel.
Tommy, in contrast to Joel, tends to be reasonably optimistic, believing he can make things better with cautious, hard work, and thus is not plagued with the same unrelenting pessimism and apathy that his brother harbors. This was his impetus for joining the Fireflies at one point, as well as why he left them to build a new life. He prioritizes his family, declining Joel's offer to take the profit from Ellie's deliverance in favor of his new family with Maria. It's rather symbolic that he married the leader Maria, emphasizing how he views the community just as (if not more) important than his brother Joel. However, after seeing his brother care for Ellie's safety, he sympathizes with the man and changes his mind, wanting to spare Joel the pain he suffered years before.
Tommy appears to be quite skilled with handguns even before the outbreak, as he kills many Infected in the first portion of the game with Joel's revolver and killed a soldier with a bullet to the head. He was also skilled in physical combat, able to kill a Runner by hitting it with a brick, and even kicked one to the floor despite it grappling Joel. Tommy also displayed great strength, being able to force a door shut despite several Runners pushing against it.
20 years later, he appears proficient with a hunting rifle against bandits, and could ride a horse at great speed and repair it's hooves when injured. He also possesses good leadership abilities, as he helps create and drive a new, less-violent community forward, being very respected within this group, while proceeding with enough caution to keep the place in order. This also affords him protection as the settlers would protect him from anyone with hostile intent, even Joel.