Daniel Koster

 was the engineer of Vault 87. He grew more and more suspicious of the secret experiments conducted in the vault, eventually choosing to confront the responsible persons after the mysterious death of his wife.

Interestingly enough, his wife, Mercia Koster, wasn't the subject of any experiments with FEV. Medical research terminal lists her as dead with code "A009", which means she had a I type cancer.

Appearances
is mentioned in Fallout 3 but does not actually appear in game.