For the playable character in the Marvel vs. Capcom franchise, see Sentinel.
Sentinels are giant robots generally programmed to hunt, capture, and sometimes kill mutants in the Marvel universe. They come in different forms, but the most typical is a large, humanoid robot, about 40 feet tall. Later Sentinel models vary wildly, and some are even able to mimic humans.
In the Marvel Universe
Sentinels were developed by Dr. Bolivar Trask to combat the so-called "Mutant Menace." When they were first unveiled, they promptly decided the best way to protect humans from mutants was to take control of the world. Dr. Trask eventually helped the X-Men shut them down, but he and other overzealous mutant-haters continue to construct them even now.