Andersen appears to have been the security chief in position when the bombs fell, having recorded several events in the security terminal. He was invited to a Halloween party but presumably did not make it out before the lockdown was put into place on October 23. He, like all other civilians inside the vault, became a ghoul.
He is in possession of the Vault-Tec control board needed for the first workshop in the vault, as Vault-Tec protocol states that all Vault-Tec control boards are to be moved into the generator room in the event of an emergency.
When the player encounters him, he has Legendary status, and as such, will mutate during combat and will drop a legendary-effect item on death, as well as the control board and any item that feral ghouls typically carry, such as junk or ammunition.