They took my wife from me, now I'll take their lives away if I don't get some answers. I've hidden some extra "help" in my safe. Accessing this message will unlock it. If I don't come back, grab that stuff and save yourself.”
Daniel Koster was an engineer in Vault 87.
Daniel Koster was stationed in a small engineering room off the atrium's upper level. He grew more and more suspicious of the secret experiments conducted in the vault, eventually choosing to confront the responsible people after the mysterious death of his wife. His safe is unlocked by accessing the last entry of his terminal.
Interestingly enough, his wife, Mercia, wasn't the subject of any E.E.P. experiments with the F.E.V. Medical research terminal lists her as dead with code "N009", which means she had a type 1 cancer.
Daniel Koster is mentioned only in Fallout 3.