Toby Nutley
From FEInfobase
Toby Nutley, an enigma to even his closest friends returned to Starfleet in 2404 without warning, the same way he left Starfleet in 2380. There was no warning before he resigned his commission as the ship passed through Sol on its way to Task Force 9 and its mission in the Gamma Quadrant.
Little is known about Toby, Starfleet has very few records of his actions after leaving Stardock in December 2380. It was almost as if he vanished from the face of the universe.
This is exactly what he wanted them to think.