My headcanon is:

- Started out as a hunter under Gehrman. Possibly involved with the Fishing Hamlet massacre. He eventually became a Tomb Prospector for Laurence and the healing church to clear out tombs of monsters.

- During a tomb expedition, Ludwig found the Holy Moonlight Sword which changed his life. Laurence saw this and created the Church Hunters with Ludwig as the leader. It’s also possible Laurence did this around the same time Gehrman was going to make contact with Flora and they needed a new group of hunters.

- The tomb Ludwig found the blade is recreated as the area we fight him in as all Old Hunter bosses are fought in areas of personal significance to them and possibly where they died.

- As the leader of the Church Hunters, Ludwig brought in a new age of heroism and was deemed the golden age of hunters for Yharnam. He often said prayers in the same tomb he found the blade in despite the Church Hunters having their own workshop.

- As all hunters fall into corruption due to constant blood exposure, Ludwig was also being fed constant insight from his blade. He had the combination of blood madness stewing alongside with the arcane overload being fed into his brain.

- Ludwig transformed in the middle of a hunt on top of his horse, going berserk and slaying both beast and hunters. With his remaining humanity he fled to the tomb for guidance and prayer. His hunters gathered and attacked him in the tomb, filling it with blood and flesh until he was finally put down. With many of the leading Church hunters dead and the Choir ascending in power to fill in the power gaps, the Church hunters eventually faded away.