Anti-mutant bigot Bolivar Trask designed the "Mark I" Sentinels to protect humanity from the "mutant threat". Unfortunately, Trask and his employees were not masters of their robots: they created the Sentinels with an artificial intelligence they could not control. The Sentinels quickly reasoned that the best way to protect humans from mutants was to control human society, instead of allowing the "imperfect" humans to do so. 
When Trask tried to order a Sentinel to seize Professor Xavier during a television debate, the Sentinel instead attacked and kidnapped Trask, taking him to the HQ Trask himself had built. The Sentinels also kidnapped X-Man Beast. The rest of the X-Men followed the Sentinels to their base, but were captured as well. 
However, one of the Sentinels left at the studio had inexplicably collapsed. Xavier discovered that a huge crystal mounted in a tower nearby had jammed this Sentinel's power unit, putting it out of commission. Xavier had his government contacts transport the crystal to the Sentinel base, where it disabled all of the Sentinels' minor units. The X-Men also managed to break free and raced to confront Trask.
Meanwhile, the lead Sentinel, Master Mold, tried to force Trask to create an army of Sentinels with which it could conquer mankind. However Trask had used a psycho-probe on Beast and discovered that not all mutants would inevitably use their powers against humanity. Understanding that he had been wrong in his prejudice, he sacrificed his own life to destroy the Sentinel-manufacturing apparatus, destroying Master Mold and most of the Sentinels in a great explosion. The X-Men barely managed to escape the base's destruction.
Controversial artist Guy DeMondue acquired three "decommissioned" Sentinels Mark I from Simon Trask for an exposition on the "mutant kitsch" in San Francisco, causing the demonstration of pro-mutants and the coming of the new-in-town X-Men. There, the depowered Magneto used tech to mimic his powers and activated two of the Sentinels to attack his old enemies, without himself to be targeted as he wasnt a mutant. One of the Sentinels was destroyed by Colossus, who threw a hybrid car on it after Wolverine had sniked it, and the other by Angel.
Robot: Due to its nature, the Sentinels were protected by the sheer strength of their armor. They could not be affected by emotional or mental attacks, nor by illusions. However, they were susceptible to attacks affecting machinery.
- Energy Blast: The Mark I could project a variety of different energy types from their chests offensively, including but not limited to: plasma, electrons, stun beams and heat. They were also armed with a disintegrator, though this only worked on inorganic matter.
- Flight: Mark I Sentinels could fly with jets mounted in their feet.
- Mutant Detection: The Sentinels constantly scanned all living beings in their immediate surrounding area and were able to determine if they were humans or mutants.
In 1973, Bolivar Trask unsuccessfully attempted to lobby Congress to approve his Sentinel program and thus attempted to seek the support of Communists during the Paris Peace Accords. However, Mystique infiltrated the meeting and assassinated Trask, starting a chain of events that led to her capture, Trask made into a martyr and eventually a dystopic future ruled by Sentinels who oppress mutants.
In a desperate attempt, Kitty Pryde sends Wolverine's consciousness back to 1973 so he could recruit young Charles Xavier to stop Mystique and avert the dystopic future she would indirectly create. However, in saving Trask, they inadvertently exposed the existence of mutants to the world. Trask then convinces President Richard Nixon into approving the Sentinel program, with the assurance that his Mark I Sentinels were made of a non-metallic polymer that were immune to Magneto's abilities. However, Magneto intercepted the shipments carrying the Mark Is and secretly inserts pieces of metal inside the robots so he could control them.
At the Sentinels' unveiling in Washington D.C., Magneto takes controls of them, using the machines to scare away the audience before dropping a stadium around the White House, the Sentinels guarding the perimeter. When Beast and Wolverine attempted to intervene, Magneto unleashed one of the Sentinels on them. Eventually, Beast injects himself with an overdose of a serum that reverted him to human form, causing the Sentinel to ignore him and focus on Magneto and Mystique, who was in disguise as Nixon, forcing Magneto to destroy it. Mystique then revealed herself by shooting Magneto in the neck with a plastic gun, stunning him and causing the Sentinels to shut down. As she turns her gun on Trask, Xavier talks her out of it and she spares his life. This leads to the Sentinel program being shut down, Trask arrested for selling military secrets and the dystopic future averted.
- The Mark I Sentinels were programmed to protect humanity from mutants, but their programming was completely open as for how they could do this. Thus, they could injure or kill humans to capture mutants.
- 18 Appearances of Sentinel MK I
- 4 Minor Appearances of Sentinel MK I
- 1 Media Sentinel MK I was Mentioned in
- 4 Images featuring Sentinel MK I
- Item Gallery: Sentinel MK I