New trailer for Re5

hey guys I have a question about  the story. I need to know before  RE5.
ok.  albert, ada, leon,  and  jill look familiar to me (take into account that I own just RE3 and RE4)

"wesker" that's his name in this forum, told me about RE 1 and 2.
but... i don't understand umbrella's purpose in  the game.
look, in the movies umbrella had military projects, I can understand that, but in the games, I just don't get it.
can anybody tell me?