The First Born Son is the ghost of Billy Michaels, and the first ghost in the Black Zodiac.
Billy Michaels loved cowboy films, and wouldn't allow anyone to keep him from them.
One day, a neighbour challenged Billy to a duel, with Billy using a toy gun. However, his plaything was no match for the real steel-tipped arrow the neighbour was using, and he died when the neighbour shot it through the back of his head...
Following his death, Billy's earth-bound spirit was captured by Cyrus to become the First Born Son.
The First Born Son was then moved to the basement of the house.
Moss encountered the First Born Son in his containment cube in the basement. The First Born Son was the sixth ghost to be released.
Several times, the First Born Son appeared before the people trapped in the house, scaring them into the clutches of the more dangerous ghosts.
Later, a Latin chant caused the First Born Son, along with the other 11 ghosts, to go to the centre of the machine and power it up.
When the First Born Son and the other ghosts were freed from Cyrus's trance, they threw Cyrus into a rotating crest of rings.
When the house exploded, destroying its walls, all twelve ghosts escaped the house and into the woods.