D'Jamat was a Triannon Pri'Nam. He was very well known amongst both Triannon factions for his religious fervor, but he had not always been such a believer. It took an encounter with the "Makers' Breath" to make him believe.
When D'Jamat was young, he fought with the Holy Regiments on the planet Triannon. He once commanded a mission to infiltrate a village known to be a stronghold for the enemy faction; his group had been assigned to remain concealed and gather information on enemy movements. They were discovered by a six year old boy; rather than compromise their mission, D'Jamat had the boy killed.
In 2152, D'Jamat led a starship of 22 other believers on a pilgrimage to the 12th sphere; they arrived in early 2153 and remained for several months. In November, Enterprise NX-01 came to study the sphere, and D'Jamat faked damage to his vessel in order to force Enterprise to rescue him and his crew.
Once aboard, D'Jamat's people used the threat of their internal organic explosives to seize control of the starship; D'Jamat planned to take it back to Triannon and use it to end the war for the benefit of his faction once and for all. He also erased 19.3 XB of data from Enterprise's computers pertaining to the spheres, and demanded that a crewmember die for this 'blasphemy'.
However, this proved his undoing; Captain Jonathan Archer tricked D'Jamat by claiming that the transporter would be used to kill him, when in reality he was just moved to another part of the ship. Doctor Phlox developed an airborne agent that would neutralize the explosives, allowing Archer to take back the ship. Archer returned D'Jamat and his people to Triannon, where they learned the war had ended in March with the decimation of both sides and the destruction of all major cities. (ENT: "Chosen Realm")