As a child, Billy was fascinated by Western films, and wouldn't allow anyone to keep him from them. One day, a neighbor taunted Billy into a duel, in which Billy used a toy gun. However, his toy cap gun was no match for the real steel-tipped arrow the neighbor was using, and he died when the neighbor shot it through the back of his head.
Following his death, Billy's spirit remained bound to earth, and was captured by Cyrus Kriticos to become The First Born Son. The First Born Son was then moved to the basement of Basileus's Machine with the other eleven ghosts. Ben Moss encounters The First Born Son in his containment cube in the basement.
The First Born Son is the sixth ghost to be released. Several times, The First Born Son appears to the people trapped in the house, scaring them into the clutches of the more dangerous ghosts each time.
Later, a Latin chant causes The First Born Son, along with the other eleven ghosts, to go to the center of the machine and power it up. When The First Born and the other ghosts are freed from Cyrus's trance, they throw Cyrus into a rotating crest of rings. The house then explodes shortly after, destroying its walls, and freeing The First Born Son and the other eleven ghosts.
- Tomahawk: Upon his death, his ghost incarnation can be seen wielding a tomahawk axe as his weapon of choice, which is ironic for him, since he is dressed mostly as a cowboy.
- The ghostly whispers which signal The First Born Son's approach are the sound of an arrow whistling through the air.
- Whenever the First Born Son is present, he tends to whisper "I want to play".
- His name in life, Billy Michaels, may be a reference to Billy the Kid due to the fact that he loved cowboy films in life.
- The First Born Son is equivalent to Aries, which is the first sign in the Black and Traditional Zodiacs. They tend to be reckless, dare-devils, irresponsible, youthful immaturity, and stubborn.
- For some reason, despite always dressing as a cowboy, his ghost is seen dressed as an "Indian", even carrying a tomahawk as a weapon.
- Whilst other ghosts appear to only travel across the ground (Cyrus being sure to put spells on the floor and the Hammer being incapable of chasing Arthur through the ceiling) The First Born Son often appears standing on walls or hanging from the ceiling.
- The Latin inscription beneath the First Born Son's symbol in The Arcanum, "Primus Filius", translates to "The First Son".
- He is the first of the ghosts in the zodiac that is male.
- His ghost file is represented by a toy gun.