The oldest of six siblings, Red has always been good at looking after other people. Born and raised in Dublin, the O'Shea family became one of many Irish families to emigrate to America ahead of the looming rationing crisis. They settled in Boston, Massachusetts, in an apartment block so full of Irish and Irish-American families that it was colloquially known as the "Paddy Quarter". Red spent much of his childhood fighting against anti-Irish sentiment; his parents were loving but overworked, so the task of protecting his siblings invariably fell to him. As an adult he made a lucrative career in Boston's illegal fighting rings, but repeated arrests eventually resulted in a court appearance and an ultimatum: enlist in the army, or face jail. He enlisted in the US Marines, where he was frequently commended for his bravery and loyalty to his battalion. Despite this, his aggression remained a problem throughout his military career.
After an incident which put three servicemen in hospital - allegedly the culmination of several weeks of anti-Irish bigotry - Red was given a punitive discharge and sent back to Boston. Unable to support his wife and newborn son, he returned to illegally boxing in order to make ends meet. Though they eventually saved enough money to buy a house in the suburbs, Red's marriage continued to dissolve, and he regularly struggled with nascent depression. The family were together when they entered Vault 111, but one researcher would later describe them as "arguing loudly enough to distress the other subjects". It was the last time they saw each other alive; when Red finally awoke from cryo-sleep in 2277, it was to discover his wife dead in an adjoining cell, and their infant son stolen by the same people who had killed her.
Now a full two centuries adrift from everyone he ever loved, Red has fallen back on all of his old habits: getting drunk, starting fights, and collecting wounds like badges of honor. Taking up the role of Mayor Hancock's bodyguard has at least compelled him to stay in one place, but the new-found access to post-apocalyptic pharmaceuticals has brought its own set of problems. Unflinchingly loyal - he rarely backs down from a fight, particularly in defense of those less fortunate than himself - Red has nonetheless spent his entire life taking blows meant for other people, leaving him damaged in more ways than a few broken bones.