He can be considered a fellow adventurer, as he mentions helping Junktown with their lights and Shady Sands with their wells, similar to what the Vault Dweller does. He's the descendant of an Americanized Celtic family with a strong desire to keep his "ethnic heritage" alive. To this end, he collects clothing, food, stories, songs, and histories as he travels the wastes. He knows the Celtic song Na Gheala Mbeadh. Patrick is determined to preserve his history.
His expertise and historical knowledge can rub off on the Vault Dweller, improving the player character's Charisma through dialogue options (requires Intelligence 7). He can also tell the player some information about different towns in the wasteland.