Jason Stryker

"My boy... The Great Illusionist!"

- William Stryker about his son Jason.

Jason Stryker is William Styker's son, and is the tertiary antagonist in X2: X-Men United. He was later adapted into the All-New X-Men comics for the mainstream universe as the new leader of the Purifiers though he is an entirely different character.

Past
Jason was Also known as Mastermind and was an earlier pupil at Mutant High. However he grew a hatred against his parents and planted horrible illusions in their minds. His mother later on committed suicide and his father brainwashed him to do whatever he desires.

X-Men 2
William Stryker uses Jason's spine fluid to hypnotize other mutants. However, it didn't work on Charles Xavier so Jason Stryker had to fool Xavier into using Cerebro by creating an illusion in which he'd be a little girl wanting to find all the mutants (so Xavier would concentrate and kill all of the mutants). Later on Magneto enters the room along with Mystique, being immune to Jason's attack due to his helmet. Magneto makes Mystique transform into William Stryker. She tells Jason to tell Xavier to find all humans instead (to kill them). Jason follows "his father's" orders and tells Xavier to find all humans. Later on Storm and Nightcrawler enters the room. Jason attacks them with an illusion of an empty room with only one little girl inside. Nightcrawler falls for it, but Storm knows it's a trick and creates a cold storm that makes Jason lose focus so Xavier realizes it's an illusion. "Jason," Xavier says with a somehow disappointed voice. The illusionary girl starts yelling "Dad is going to be so mad at me!" and starts screaming, which breaks the illusion. Xavier turns around and looks at Jason with a sympatric look. Then Xavier leaves the room along with Nightcrawler and Storm and Jason is left behind to die as the dam falls apart.

X-Men 3: The Official Game
In the video game; X-Men 3 the Official Game; Jason somehow survived and tried to finished what his father started. He did this by unleashing the Master Mold, a giant robot that could create Mutant-Eliminating Robots known as Sentinels. He also attempted to break Nightcrawler's mind by telling Kurt that he left him to die. When the X-men were attempting to shut down and destroy the Master Mold, It turns out that Jason as a second personality, one that wanted to help Nightcrawler destroy the Master Mold. After the Master Mold was destroyed, Jason told Kurt to leave his body so he could finally be at peace.

Trivia

 * Jason Stryker actually makes a cameo is X-Men Origin: Wolverine.
 * Jason Stryker's film version is based off Mastermind/Jason Wyngarde from the comics.
 * In the comics Sryker's son who was originally an unnamed infant that was killed by his father shortly after birth when he recognized that his son was born as a freak. Later in the All-New X-Men comics this was retconned to where it was revealed that the child was still alive (after his father took him to A.I.M. to have his condition treated) and had taken over leadership of the Purifiers.