The Jefferson Sovereign is driven by the game's co-protagonist: Taurus. He frequently uses the nickname Eloise when he talks about his ride.
The Sovereign is a monster of a car; one does not drive it as much as navigate it. Its mass and firepower make up for its poor handling. Eloise is silvery-grey all over, with a leather interior and a pair of real bull horns mounted on the hood. Taurus doesn't explain the name, but it's a safe bet it's connected to his mysterious past.
The Jefferson Souverign is based on the real world 1969 Lincoln Continental.