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.
If the Vault Dweller asks Patrick if they know the song "Na Gheala Mbeadh," he will sing it, adding 1 point to the player character's Charisma through dialogue options (only happens the first time one talks to him, which requires a Speech check. One can try multiple times by cycling through the dialogue). It requires an Intelligence of 7 or higher to unlock the dialogue option..
He can also tell the player character some information about different towns in the wasteland.
If the player character finds this encounter at night, there will be a beer bottle on the ground close to the fire. Using the Steal skill on the bottle will give you access to Patrick's inventory.