General Harper was one of several generals stationed in the Whitespring bunker when the bombs dropped. After Secretary of Agriculture Thomas Eckhart had himself nominally elected president, he held a vote on whether to continue the war with China. Those who voted for continuing the war lined up near the room's only exit and those against lined up at the far wall. After the pro-war voters left, everyone still inside was gassed by MODUS on orders from Eckhart. Harper, being the only general that voted to continue the war, became integral to Eckhart's plans. He ordered MODUS to assign an escort to Harper around the clock, while scouts were to keep out an eye for potential candidates for "recruitment."
After N. Jackson discovered the way to get inside the Appalachian missile silos, the Enclave held a staff meeting that Harper attended. He questioned the motive behind the mission, and how many men would be mobilized just to vote for Thomas Eckhart and grant him the title of president. However, Eckhart believed it was necessary to give the men of the Enclave an authority to look up to.
Despite this, Harper remained loyal to Eckhart and continued to act as a significant military advisor to him. However, he died in 2083 from radiation poisoning, as Eckhart's desperate attempts at resuscitation were unsuccessful.
T. Harper is mentioned in Fallout 76.