Mr. Callahan, along with his wife, was one of the citizens of Sanctuary Hills to be elected as a resident in Vault 111. He made it in time to enter the vault before the nuclear bomb exploded. He died of asphyxiation within the cryo-chamber due to the life support to the pods being switched off, during the Institute's kidnapping of Shaun in 2227.
The overseer's terminal mentions a malfunction in Pod C3 where the occupant had heart palpitations and nearly thawed out, and refers to the occupant as "her" even though Mr. Callahan is the dweller assigned to this pod.
Mr. Callahan appears only in Fallout 4.