Sentinel with Wolverine
It was fear that drove Bolivar Trask to create the Sentinel Program. He had studied the history of human development, and hypothesized that the rise of mutants meant the end of humanity as we knew it. The trajectory of the future awoke in him a gut-wrenching terror - one that guided wvery decision he made for years. The discovery that his own son was a mutant only confirmed his fear.
The solution Trask created was an enormous machine - a multistory engine of destruction. Thirty feet tall, Trask's SENTINEL robots were capable of high speed flight, and wielded powerful cincussive energy blasts with deadly precision. Though Trask quickly came to realize his mistake, the legacy of his fear lives on in the software that allows these robot hunters to detect and disable mutant powers, and the mighty weapons they carry.
The X-MEN have faced these destructive machines countless times, and each encounter has been more dangerous than the last. As technology has improved, each generation of SENTINEL has become more effective at its primary task - the destruction of all mutants. The margin of victory for the X-MEN has become more and more narrow in every battle until every mutant has come to believe that it is only a matter of time before even the X-MEN are overcome, and Trask's terrible dream becomes reality.
* All Character biographies/descriptions are from Marvel Universe figure packaging.