William Yates was a Starfleet lieutenant serving 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.
Yates was killed in 2375 as the result of retaliatory attacks on the Equinox crew by a series of nucleogenic lifeforms, whom the crew had been murdering for the purpose of converting the remains into a source of fuel. After the surviving Equinox crewmembers were rescued by the crew of the USS Voyager, Yates's name was mentioned during a memorial service aboard that ship. (VOY: "Equinox")