(covers information from an alternate timeline)
H. Dunbar was the assistant to Henry Starling, CEO of Chronowerx Industries, in the 1990s. In that capacity, he worked to assist Starling in his efforts to exploit technology cannibalized from the 29th century timeship Aeon, which Starling had discovered crashed in 1967.
In 1996, Dunbar, on Starling's orders, attempted to kill Rain Robinson, an astronomer in Starling's employ, who had discovered the presence of the USS Voyager, which had accidentally traveled back in time from the year 2373, in Earth orbit. Later, after Starling had been apprehended and detained on Voyager, he successfully beamed Starling back to Chronowerx headquarters, using the Aeon's transporter and a Chronowerx satellite.
In an effort to lead the Voyager crew to believe that Starling was planning on launching the Aeon from a remote desert location, Dunbar drove a tractor trailer away from Los Angeles, using a temporal transponder set to give off tachyon signals, to fool them into thinking that he was moving the timeship, when, in actuality, Starling was planning to launch from Chronowerx headquarters. Dunbar was pursued by Rain Robinson and Tom Paris, who attempted to use a phaser to immobilize Dunbar's vehicle. Dunbar remained in control of the truck, however, and attempted to run down Rain and Paris, but was killed when his truck was destroyed by a shuttle piloted by Commander Chakotay and Lieutenant B'Elanna Torres. (VOY: "Future's End", "Future's End, Part II")