Vault Dweller

In a general sense, a vault dweller is just a dweller of one of the Vault-Tec Vaults.

When capitalized, the Vault Dweller is the main character of Fallout 1 and the grandfather of the Chosen One, the main character of Fallout 2. He sent out by the Vault 13 Overseer on a misson to find a replacement for the Vault's broken water chip. In the course of his adventure, he ended up defeating the mutant threat (by destroying the vats) and assasinating the Master, and the leader of his cult, the Children of the Cathedral's Morpheus.

Note that while in FO1 the player could choose to be either male or female, the canon Vault Dweller, as established by FO2, was male.