SPOILER:
Alcatraz is a Force Recon marine, part of a team of U.S. Marines deployed shortly after the alien invasion in New York City. Their original mission was to locate, secure, and exfil Dr. Nathan Gould, one of the original chief researchers at CryNet/Hargreave Rasch, the creators of both NanoSuit 1.0 (Crysis 1) and Nanosuit 2.0 (Crysis 2).
MAJOR SPOILER:
Later in Crysis 2, you'll discover that Hargreave tricked Prophet in Crysis 1 into putting on Nanosuits in the first place. It turns out Nanosuits have some sort of user-resistance, and over time, if the Nanosuits are exposed to alien viruses, the suits will reject the human user, sort of like how human immunodeficiency virus (HIV) will eventually decay the body into death. So Nomad, Psycho, they both died in the time between Crysis 1 and Crysis 2 due to nanosuit resistance.
Prophet's suit is superior, allowing whoever wears it to survive longer. Unfortunately for Prophet himself, his time had ran out so he gives his suit to Alcatraz, who carries on his work. The deep layer substrate in his suit acts as a synthetic habitat to cultivate a vaccine against the Ceph virus.
When Prophet discovers this, he calls out on Hargreave.
Hargreave: "You have to go back, Prophet!"
Prophet: "I don't understand..."
Hargreave: "The suit. Your suit has learnt the Ceph's systems, you have to go back."
Prophet: "You.. twisted.. mother ****. You knew! You knew what the suits would do to my men! You turned them into dead men walking!"
Hargreave: "I turned them into post human soldiers. You're a soldier, think of it as a necessary sacrifice--"
Prophet: "YOU. LIED TO US." *slams fist on table in honest rage*
Hargreave: "Perhaps I was being a little economical with the truth. But what choice do you have? This isn't a war ordinary soldiers can face. This is the future. Death is a mere inconvenience now, nothing more. It is just a matter of time now. We are all DEAD MEN WALKING" *fade out*