Laurentius was a student of pyromancy in his home, the Great Swamp. He considered turning Undead to be beneficial as it prompted him to travel to Lordran where pyromancers earn a certain respect. The Crestfallen Warrior calls him an "old man" despite him looking and sounding like he is in his thirties at most.
If the player acquires pyromancies from The Fair Lady or Quelana of Izalith or upgrades their flame with Quelana, he will ask the player where they obtained such power. If the player answers "Yes" to his question, he will travel to the Blighttown where he is later found hollow in the swamp. If the player answers "No", he will remain in Firelink Shrine as a merchant and pyromancy trainer.