Sentinels are a variety of mutant-hunting robots, appearing in the Marvel Comics universe. A Sentinel appears in X-Men: Children of the Atom, Marvel vs. Capcom 2: New Age of Heroes and Marvel vs. Capcom 3: Fate of Two Worlds.
The Sentinels were invented by Dr. Bolivar Trask after he found that his own son had developed mutant powers. After being unable to suppress his son's growing mutant powers, Trask studied the nature of powerful mutations and came to the conclusion that mutants would eventually supplant normal humans as Earth's dominant race if no action was taken to control them. Soon after, Trask and a team of scientists developed the first Sentinel prototypes in a secret laboratory, intending to use them to capture and destroy America's mutants in an ambush. However, Trask realised that not all mutants were hostile to humans, and helped the X-Men to destroy his Sentinel manufacturing facility.
Since then, the majority of Sentinel designs and manufacturing is now under United States Government control, being used to aid the US military on some occasions in operations against mutants, and are constantly refined and improved in order to maintain their high degree of lethality. However, numerous cases exist where Sentinel designs and manufacturing secrets have fallen under the control of various villain organisations.
Though Sentinels are commonly seen as autonomous robots, some manned models have been developed, with the Sentinel's chest area housing a cockpit for the pilot. In addition, the anti-mutant protocols developed for autonomous Sentinels require them to protect humans from mutants, though their combat programming gives Sentinels a high degree of leeway as to how they do this. Thus, massive collateral damage is often the norm when Sentinels are deployed to capture or kill mutants.