This is a Town NPC. A House may be required in order for it to appear.
The White Mage is a Town NPC that does not have any requirements (except for a house) to appear.
At start: Lamp Tome, Pure Tome,
After first boss:Cure 1 Tome, Heal 1 Tome,
Hardmode world: Cure 2 Tome, Barrier Tome, Heal 2 Tome, Dezone Tome.
Golem Defeated: Cure 3 Tome, Wall Tome, Heal 3 Tome