Na'kuhl

The Na'kuhl were an alien race from the 29th century, and a faction in the Temporal Cold War, vehemently opposed to the Temporal Accord. They were led by Vosk, a dangerous fanatic who viewed time travel as his innate right, despite the damage that might be done to the timeline.

Sometime in the 29th century, the Na'kuhl fleet fought a large battle against Starfleet and the Vorgon. When the Phoenix-X travelled into this battle, Lieutenant Amp, a computer virus, was used to cripple the Na'kuhl fleet by infecting the ships' computer systems. This infection was able to filter into every ship, then causing permanent damage to the Temporal drives on those Na'kuhl vessels with time-travel ability. By this time, nearly all Na'kuhl time-travel ability was wiped out - except for the ship in which Ghrath was employed. (: "Temporal Doom! Part III")

Ghrath used his last-remaining time-travel device to travel back to Earth in the 1940s and infect the timeline. ( "Storm Front")