Tom was Dave's father and the original leader of the Kingdom of Tom, the small settlement that is now the Republic of Dave. He was apparently a ruthless dictator that Dave managed to overthrow due to his extremist leadership tactics. Dave managed to take the land and created a democracy for his two wives and children, plus the other inhabitants that remain there.
Whether Tom was killed, cast out, or simply remained in the new Republic of Dave until he died of old age is not known.
Tom is mentioned in Fallout 3.