Father Elijah is the main antagonist of the Fallout: New Vegas expansion Dead Money.
He was the leader of the Brotherhood of Steel in the Mojave Wasteland, but prior to the start of the game he got most of the Brotherhood killed by the NCR at the HELIOS One power plant while trying to find the ARCHIMEDES laser weapon, and was then fired and disappeared and hasn't been heard from since. Veronica Santangelo, one of the Courier's companions, looked up to him as a father figure and believes he is still alive and doing something important.
Dead Money Secret Ending Tutorial