I Am Legend

Will Smith plays (as far as his character knows) the last man on earth, our hero, Robert Neville, a sole survivor of a world dominating virus created by man, that initially takes out 588 million people in 2009, and was originally created to somehow cure cancer. In 2012, Neville (a former scientist) dedicates his life to surviving for the sake of the human race, since he's somehow immune to the virus and those who have been infected, and attempts to find a cure. In order to find a cure, he seeks out the infected beings at night, who seem to have completely forgotten how to act human, their instincts and survival skills have become non-existent, and either takes them out to survive, or in some cases, drags them to his underground lab for research purposes, in hopes of correcting humankind's mistake.