Jill Valentine is a member of the Special Tactics and Rescue Squad (S.T.A.R.S.). Jill survived the mansion catastrophe but is still stuck in Racoon City. Resident Evil 3: Nemesis takes Jill through her story to get out of Racoon City.
She gained the title "master of unlocking" because of her past as a thief. She survived the mansion incident in the first game (Resident Evil).
 Death Speculations
It's been confirmed that Jill Valentine isn't dead in the Resident Evil 5 game.