The Sentinels are the ultimate mutant-hunting machines, plaguing the lives of the X-Men - but the first versions were created to take down Captain America. Created by the scientist Bolivar Trask, the Sentinels were envisioned as the ultimate mutant-hunting machines. These towering androids contain sophisticated technology allowing them to identify mutants, and they proceed to eliminate them with extreme prejudice.
The Sentinels are undoubtedly the greatest enemies of the mutant race, in part because every generation of Sentinel is more dangerous than the last. Rogue Sentinels were responsible for a horrific act of genocide when they launched an attack on the mutant nation Genosha, killing over 16 million mutants in one attack. The ultimate Sentinel is Nimrod, initially encountered by the X-Men due to time travel but recently created in the main Marvel timeline. According to resurrecting mutant Moira MacTaggert, the mutant race is doomed to die in every timeline where Nimrods are forged.
Surprisingly, though, the first generation of Sentinel-like androids were created not to deal with mutants - but with super-soldiers. According to Captain America annual #8, by Mark Gruenwald and Mike Zeck, the U.S. government pursued Sentinel-like technology at the same time as Captain America's super-soldier program. It's important to remember Steve Rogers was never supposed to be the only super-soldier; the government believed an army would be needed to fight on the front lines of World War II. They feared these super-soldiers would be unable to adapt to peace-time conditions, and thus began experimenting on Sentinel-like androids to neutralize them should they get out of control. In 1939, a scientist named Daniel Schumann successfully created a prototype called TESS-1 - the acronym standing for "Total Elimination of Super-Soldiers."
TESS-1 largely depended on brute force to neutralize threats, and lacked the sophisticated armaments of Sentinels. Still, the concept is the same; an android created purely to deal with superhuman threats, envisioned as a shield between baseline humans and people with powers. The project was shut down after the death of Abraham Erskine, because the U.S. government saw no need to develop an army of androids to deal with a single super-soldier of good character - and then Steve Rogers was believed killed in action, in reality becoming trapped in the ice for decades. The idea would, of course, be revisited when mutants began to emerge and super-powers became commonplace.
TESS-1 was eventually discovered by a mutant who possessed the power to control machines with his mind. Burning with a deep-rooted fear of nuclear war, he attempted to destroy the United States' entire nuclear arsenal; he was defeated by Wolverine and Captain America, although he did take the time to try to give TESS-1 an Adamantium-based upgrade. Fortunately the two superheroes deduced TESS-1's joints would be vulnerable, and they took it down.
It's ironic than Captain America teamed up with the X-Men's scrapper to defeat the android that seems to have been an ancestor of the Sentinels.