Father Elijah

 was an elder and leader of part of the west-coast Brotherhood of Steel.

Background
He went missing during the NCR takeover of the HELIOS One powerplant and was never found. According to Head Paladin Hardin, his becoming an elder was questionable due to his status as a scribe; normally, the ability to become an elder is reserved for Paladins, though in Elijah's case an exception was made due to his high intelligence. Veronica refers to him as still alive as he contacted her after the HELIOS One disaster. However during the quest I Could Make You Care there is a skeleton in Gibson's Shack, which is the location that Elijah was living within (or at least communicating from). Though that does not necessarily mean it is the body of Elder Elijah, the condition of the residence is indicative of an area raided by tribals, including the apparent murder weapon, a machete. Father Elijah will appear in the DLC Dead Money.

During the quest Still in the Dark, after talking to some of the members of the Brotherhood of Steel, you find out Elijah became an elder because he was a genius. However, the members say he was a strange man and his battle tactics were poor. They then tell you during the takeover of HELIOS One he held them inside the building too long. He kept saying something was almost ready. Perhaps this is hinting to the Archimedes II.

In the add-on, Dead Money, it is revealed that Father Elijah discovered the Sierra Madre whilst searching for weapons to eradicate the NCR. It is hinted at that he is the person who activates the radio signal luring the player to the Sierra Madre, possibly meaning you may get to meet him.

Appearances
is only mentioned in Fallout: New Vegas.