Created by noted anthropologist Bolivar Trask, the first Sentinels were lumbering, semi-humanoid robots tasked with the apprehension or elimination of mutants. Although Trask's principal field of expertise was anthropology, he also demonstrated considerable talent in the areas of biophysics, cybernetics and robotics. When his young son, Lawrence, developed precognitive abilities, Trask embarked on a privately funded anthropological study of the rapidly increasing, worldwide emergence of genetically empowered individuals. He became convinced that these mutants, the first of a newly evolving race, would use their powers to dominate the world and enslave mankind. Trask eventually founded a small group of researchers, led by himself and his now-adult son, to compile evidence that mutants posed a threat to humanity. Drawing on his considerable fortune, Trask hired a large team of cyberneticists, roboticists and engineers to realize his designs for the ultimate solution to what he perceived as a global dilemma.

Trask publicly revealed the existence of the Sentinels during a live, televised debate on the alleged mutant menace with Professor Charles Xavier -- secretly the telepathic leader of the heroic band of masked, mutant adventurers known as the X-Men. The Sentinels were programmed to protect mankind from mutants, but cold logic led them to conclude that they could best accomplish this aim by seizing control of society from the imperfect humans they considered to be their inferiors. One of the Sentinels attacked and kidnapped Trask during the debate, countermanding his orders. The Alpha Sentinel, Master Mold, attempted to force Trask to construct more of its kind, so as to facilitate the androids' conquest of the human race. Training a thought-reading probe on the ape-like X-Man called the Beast, Trask realized that not all mutants would inevitably use their powers to subjugate humanity. Finally grasping the magnitude of the evil he had wrought, the scientist sacrificed his life to destroy Master Mold.

Following Bolivar Trask's death, his son spearheaded construction of the Mark II Sentinels. Wrongly blaming the X-Men for his father's fate, Larry Trask targeted the outcast adventurers for capture and imprisonment. When the medallion that suppressed Trask's powers was removed, the Sentinels realized that he was a mutant and declared their autonomy. In effect, they had become their own masters. The Sentinels computed that the best way to halt human evolution was to destroy the sun, the source of most mutation-inducing radiation on Earth. While orbiting their target, however, they concluded that they lacked the means to destroy it. The Sentinels returned to Earth to implement a new set of tactics, but were put down by the Avengers. Earth's Mightiest Heroes deactivated or destroyed most of the robotic executioners. Trask died during the battle.

The U.S. government took ownership of the Sentinel plans following Trask's death, and Dr. Steven Lang was placed in charge of a federal investigation into the origin of genetic mutation. Unknown to his employers, Lang's objectivity was skewed by a fanatical, irrational distrust of mutants. He used his position to acquire Trask's designs and notes, then sought financial backing from the Hellfire Club, an elite social organization of the world's wealthiest and most powerful figures. In pursuit of its goal of world domination, the Hellfire Club provided Lang with funds to construct new Sentinels and an orbital space station -- not knowing that he intended to terminate every mutant abducted. Unfortunately for Lang, his first captives were the X-Men. The heroes escaped their bonds, and destroyed Lang's Sentinels and space station.

After the terrorist organization called the Brotherhood of Evil Mutants attempted to assassinate Senator Robert Kelly, the president inaugurated the secret and illegal operation known as Project Wideawake to apprehend and detain genetically empowered individuals. The government contracted Shaw Industries to construct Sentinels in secret -- unaware that the company's owner, Sebastian Shaw, was himself a mutant. Without the government's knowledge, Shaw used the Sentinels to attack the X-Men in his role as leader of the Hellfire Club.

The next Sentinel threat would originate in an alternate future where the mutant-hunting robots reigned supreme. Nimrod, a state-of-the-science Sentinel, traveled back in time -- emerging in the present to hunt mutants as he had in the future. The X-Men neutralized Nimrod, but his technology merged with that of Master Mold. The amalgamated android battled the X-Men, who were able to defeat the robot only by forcing it through the dimensional portal called the Siege Perilous. The magic of the Siege Perilous would allow any entity that passed through it to be reborn as a new being. Nimrod returned in humanoid form as Bastion and began to integrate Sentinel technology into unsuspecting humans.

These sleeper agents were unaware of their programming, awakened only by mutant activity. Privately re-establishing the Sentinel program, Bastion received government sanction to commence Operation: Zero Tolerance. Commanding a hidden army of Sentinels, he ransacked and razed the X-Men's mansion, downloading Xavier's extensive computer files on mutants around the world. Bastion used this information to systematically attack and capture the X-Men and their associates. The android ultimately was destroyed, but the X-Men found it difficult to locate and deactivate all the humans he had transformed. The mutant heroes could not attack these cyborg Sentinels in wanton fashion, as they were victimized humans -- a weakness on which Bastion likely had counted.

The latest mutant-hunting androids, the product of a shadow-ops program, assimilate automobile and aircraft components, machine parts, and building materials to keep pace with genetic mutation. As humankind inches toward extinction, the Sentinels gather in secret enclaves throughout the world -- waiting to pounce on an unsuspecting mutant population.

First Appearance: X-Men (Vol. 1) #14