Brian Sofin was a crewmember aboard the USS Equinox under the command of Captain Rudolph Ransom in 2371. In that year, the Equinox was stranded in the Delta Quadrant by the alien entity known as "the Caretaker."
As a member of the Equinox crew, Sofin participated in criminal experiments to augment their warp drive by murdering a series of nucleogenic lifeforms and converting their remains into a source of fuel, presenting the crew with the opportunity to return to the Alpha Quadrant in mere months. In 2376, after the death of Captain Ransom and the destruction of the Equinox, Sofin was integrated into the crew of the USS Voyager, another Starfleet vessel which had been stranded in the Delta Quadrant, along with four other Equinox crewmembers. As a consequence for their actions against the alien lifeforms, they were stripped of rank, their privileges were severely limited, and they were expected to work under extremely close supervision. (VOY: "Equinox", "Equinox, Part II")