Wilhelm Garrett was a 24th century Starfleet Officer who served aboard several starships as well as teaching counterintelligence and small unit tactics at Starfleet Academy.
He was a man who kept meticulous logs and notes on everything, attributing it to the memory loss of his early childhood, saying he didn't want to forget anything, ever again.
In 2331 the USS Taurus responded to a distress call from a Federation colony along the Neutral Zone. By the time it arrived, along with the Excelsior and Hathaway, the colony had been destroyed. Thirteen children, ranging from ages seven to sixteen were found in a cave outside one of the settlements, all undernourished. They were taken aboard the Taurus for medical treatment.
Medical tests revealed that he had been born in 2328, though the trauma he'd suffered kept him from remembering more than his first name and a handful of details from his earlier life, a condition that was widespread around all of the surviving children.
He was adopted by the ship's Second Officer, Lieutenant Commander Felix Garrett, and the two traveled to Earth shortly afterward. Once there, in the city of San Fransico, Wilhelm was raised as a member of the Garrett family, alongside foster siblings Ronald and Miranda.
He graduated with honors and was assigned to the USS Charleston as a helmsman.
Wilhelm continued to serve on starship duty, eventually rising to the rank of Commander and serving as XO of the USS Innsbruck.
In 2368 in left starship duty to become an instructor at Starfleet Academy, teaching courses in Survival, Counterintelligence, and Small Unit Tactics.
In 2371 he was at odds with his department chair, Professor Pembleton, over changes he wished to make to the curriculum. When George Foster took over as superintendent that year, he chose Garrett as his attache since Tachion had already accepted command of the USS Lionheart.
Garrett was in fact one of several children who were kidnapped by Romulans and raised on Romulus to be loyal to the Empire. When the boy was old enough, nine or ten, having completed his conditioning, the Tal Shiar staged an attack on a Federation colony close to the Neutral Zone, and left several of these children behind, for kindly Starfleet officers to pick up. No one suspected that Cmdr. Garrett was a Romulan spy, working secretly for the Tal Shiar. His counterintelligence lessons were always just slightly "off", which trained Romulan officers would notice, and realize the suspect was a Federation agent. Starfleet lost many under-cover agents because of Garrett. He was always very careful, and passed his notes off to a contact only once a year. The Tal Shiar had an escape route in place, just in case Garrett was discovered, but Sela and the other high Romulan Tal Shiar did not wish to lose such a valuable asset, so highly placed in Starfleet Headquarters. ("The Way of Dera," boxed set, Star Trek the Roleplaying Game, by Last Unicorn Games, 1998.)
His daughter enrolled in Starfleet Academy in 2371 and was a member of the institution's rugby team.