Stephen was one of the mutant children genetically engineered by Zander Rice as part of Project X-23. Rice used genetic samples from mutants to create new embryos that were carried by unidentified Mexican women.
The mutant children were supposed to become soldiers, but were deemed failures after the creation of X-24. After the X-24 project was a success, and the X-23 Project a failure, Transigen scheduled all the other subjects for termination. With the help of the nurses, who had grown attached to the children, the mutant children escaped to find Eden, a safe haven for mutants in North Dakota, while Laura was spirited away and adopted by her nurse, Gabriela Lopez.
When Laura finally made it to Eden, with her biological father Logan, Logan collapses from injuries he endured along the way. Stephen and the other mutant children nursed Logan back to health.
Two days later, while Logan, who fully healed, was asleep, Bobby, Stephen, Charlotte, and Gideon, use pairs of scissors to trim off most of Logan's beard. When he awakens, he sees the mutant children present giggling, feels his beard, goes to a mirror, and sees that some of the children trimmed it off, and tells them that it's not funny. Logan notices Rictor walking up the stairs, and asks how long he's been out, as the two mutants exit the room.
The next day, Stephen begins his hike through the woods to cross the Canadian boarder, along with the other mutants so they can be safe. Unfortunately, Donald Pierce, the head of security for Alkali-Transigen, and the company's security team, The Reavers, are in pursuit to stop them. Stephen and the other kids, except Laura, were eventually captured by the Reavers and then confronted by Rice. However, Logan, who saw the Reavers following through the hideaway, then shows up to save him and the others.
After Logan kills Rice by shooting him, the kids escape and help defeat some of the Reavers, before Pierce releases Logan's savage clone X-24 to kill Logan. When Pierce to tries to help X-24 in the fight, Stephen then watches as Joey, Bobby, Delilah, Charlotte, April, Jonah, and Mira to use their powers to kill him. However, X-24 eventually wounds lethally wounds Logan and nearly kills him, until before Laura shoots him with an adamantium bullet Logan kept, killing X-24. Stephen sadly watches Logan die from his wounds, then he and the other kids have a funeral for him. Stephen and the kids then continue with their hike to cross the boarder.
- Power Detection: Stephen can detect mutant powers.