Once an upstanding officer of the law in NCR, Jack's life took a turn for the worse when his marriage with Mira crashed horribly. His wife managed to coerce the court into giving her almost everything they worked together for and that still wasn't enough - she wanted him dead. Jack has since gone deeper and deeper into depression, building up anger inside him.
One day in the 2240s he finally snapped, and after grabbing a brick of plastique, he wired himself to the town's power generator, threatening to blow himself and the generator to kingdom come.
"Take care of Officer Jack" for Mira: Jack is first encountered as he threatens to blow up the NCR powerplant. Several options are available for dealing with him: one, reason, though unlike most, only the most hostile dialogue options will make him reconsider his position. Second, he can be shot to death, which will not make Dorothy happy, as she understood that the poor man snapped due to pressure. Last, he can be allowed to blow up and the city generator either fixed or left disabled (energy fields throughout the city go down as a result).