The blacksmith deity forged the weapons of other Gods, possibly from Titanite.
The Demon Titanite description reads:
Special titanite stolen from a faceless stone beast known as a Titanite Demon.
When the nameless blacksmith deity passed, from several Slabs, great beasts arose.
The power of titanite remains within them, and they still roam Lordran today.
This implies that the Titanite Demons, also known as Prowling Demons across Lordran came to life from Titanite that this Blacksmith deity left behind.