Colonel William Stryker is the main antagonist of X-Men 2 and X-Men: Origins Wolverine and the tertiary antagonist of X-Men: Days of Future Past.
X-Men: Days of Future Past
Stryker is Bolivar Trask's right hand man and the tertiary antagonist in this film, which focuses on the beginning of Stryker's education into mutant affairs.
X-Men: Origins Wolverine
In X-Men Origins: Wolverine, Stryker is the main antagonist. William Stryker is a ruthless military man in charge of an illegal project to experiment on mutants to harvest power for a mutant-killing "Deadpool" - to this end he imprisoned many young mutants, including Scott Summers, and manipulated Wolverine as well as his superiors. Stryker was emotionally scarred from his past, when his son killed his wife due to mutation and grew to see that most mutants were given a curse. Stryker eventually met Wolverine and Sabretooth in a prison cell. He offered the two to join Stryker on a team which consist of other mutants, including; Agent Zero, John Wraith, Wade Wilson, Christopher Bradley, and Fred Dukes. He set this team up so he could discover the location of a metal substance known as Adamantium. When Stryker and his team were holding an entire village in Africa hostage, he threaten to kill the entire village if they don't tell them when the rest of the adamantium is. Refusing to answer Stryker, Stryker demanded the mutants to kill the all. However, Logan intervened and them that he didn't sign up of this. After which, Logan quit the team.
Sometime within the six years that have gone by, Stryker and the remaining team managed to find the adamantium. He also managed to figure out how to manipulate adamantium. Stryker was also starting to hunt down other mutants. With this, most of the team members including Wraith, Bradley, and Dukes quit as well. Only Agent Zero stay by Stryker's side. Stryker also managed to locate where Logan's been hiding, so he blackmailed another mutant name Kayla Silverfox to manipulate Logan to fall in love with him. If she didn't he would kill her sister. Starting to put the pieces together to create the mutant killer, Stryker "killed" Wade to use his body to create the Mutant Killer. He also made a deal with Sabretooth that if he helps Stryker with his goals, Stryker would surgically implant the adamantium on his skeleton. A few days after Wade was "killed" Stryker sent Sabretooth to kill Bradley.
A few days after Bradley was killed, Stryker, along with Agent Zero traveled to Canada where Logan was living. He informed Logan that Wade and Bradley were killed. He made a partial lie to Logan that he believed that someone was hunting down their old team, and that Victor was safe. He offered Logan protect, but Logan didn't want anything to do with it. The next day, Stryker sent Sabretooth to "kill" Kayla. After finding Kayla "corpse", and got brutally beaten by Sabretooth, Logan encountered Stryker at the hospital. Logan immediately knew that he knew that it was his brother was the one who's been killing their old team. Stryker made him an offer that he can give him the tools that can kill Victor. The two traveled to Alkali Lake where they implant the adamantium onto Logan's Skeleton, as well as give Logan some new dog tags labeled "Wolverine". After the bonding was successful, Stryker processed to create the Weapon XI. He also ordered the termination of Logan. However, thanks to his heighten sense of hearing, Logan overheard them. Enraged, Logan managed to escape the base while killing a few of the guards. Stryker then ordered Zero to kill Logan.
The next morning, Zero managed to locate Logan, and sniped down an elderly couple who befriended Logan. He then informed Stryker that Logan killed two civilians. Stryker demanded that Zero to kill Logan. However, Logan managed crash the helicopter that Zero was in. Logan then warned Stryker that once he's done with Victor, he's next, processing with killing Zero.
While Logan was trying to figure out Stryker's plan, Stryker managed to locate a mutant that generate an optic eye beam from his eyes; Scott Summers. So Stryker sent Victor to capture the young mutant. After successfully capturing Scott Summers, Stryker sent him The Island.
After discovering what Stryker's plan, including figuring out that Victor was working for Stryker, Stryker attempting to create a mutant killer, and the location of his hidden base known as The Island, Logan, with the help of Gambit, traveled to The Island to kill Stryker. During this, Stryker and a group of surgeons were working on the Weapon XI aka Deadpool. When Logan managed to reach Stryker, he demanded he to tell him why he did all this. Stryker explained that he did this so humans could have a fighting chance the mutant kind. He also informed that revealed that Kayla was still alive. Stryker demanded that she tells Logan happened the day she "died", while at the same time making it look like she never loved him. She explained that Victor injected her with hydrochlorothiazide to make her heart drop so low it almost looks like she flat lined. He then poured blood all over her body to make it look like she was killed. Stryker then explained that Kayla was a mutant as well with the ability of Tactile Hypnosis. Confused and upset, Logan left the laboratory believing Stryker's lies. After Logan left, Kayla demanded Stryker to release her sister since she held up her end of the deal. However, Stryker made up an excuse to keep her sister locked up. Just then Victor showed up in an angered state. Victor demanded Stryker to implant the adamantium inside him . But Stryker made another excuse saying that Victor would never survive the procedure. Kayla then realized that Stryker was using them as he had no intention to hold either one's deals. Despite this, Victor still wanted to serve Stryker until the Adamantium was surgically placed on his skeleton. Just as Victor was about to kill Kayla, Logan came back to fight his older half-brother. During this Stryker unleashed Weapon XI to engage and kill Logan. Just as Stryker commanded Weapon XI to decapitate Logan, Victor showed up and save his half-brother, implying that no one kills Logan but him.
After the to managed to "kill" Deadpool, Stryker shot down Wolverine with adamantium bullets in hopes to either kill him, or have his memory wiped out. After Stryker was successful, he attempted to kill Silverfox, but she used her mutant abilities to have him walk until feet bleed, and continue walking afterwards. Some time later, Stryker was detained for questioning by military police in connection with the murder of General Munson.
in X2: X-Men United ,Stryker appears as the main antagonist again. 15 years later, Stryker had a new plan to wipe out all mutants. He started this plan by using his son's mutant ability to brainwash a mutant Deathstrike to be his bodyguard and increase her skeleton with adamantium. He then managed to convinced the President to legalize an Anti-Mutant program, by brainwashing Nightcrawler to attack the President. While he was doing all that, he also brainwashed Magneto to have him tell Stryker all about Cerebro. Stryker kidnaps many of Xavier's students and then Xavier himself in order to build a Cerebro-2, utilizing his own son and he forces Xavier into tracking down all mutants on Earth with the intent of killing them all, in retaliation Magneto tries to use the same device to kill all humans on Earth. This caused Stryker to be shocked because Magneto use the device against him. The X-Men stopped the device and destroyed it. Magneto hung Stryker to the wall to make sure he never do this again. Wolverine confronted him one last time until the dam collapsed and thus killing Stryker.