A Starfleet lieutenant aboard the Enterprise-D who kills himself in 2370 by leaping into the plasma stream of a warp nacelle, prompting an investigation by Deanna Troi and Worf.
Lieutenant Daniel Kwan appears in the seventh-season episode Eye of the Beholder. He works in nacelle control and, as far as anyone knows, is content: well regarded by his superiors and happy with his girlfriend, Ensign Calloway. His sudden suicide makes no sense to the crew.
Kwan's mother was Napean, which gave him a degree of empathic sensitivity. Troi discovers that this was his undoing. An empathic imprint left in the nacelle structure eight years earlier, during the ship's construction at Utopia Planitia, overwhelmed him with another man's despair.
Troi, herself an empath, is caught by the same echo and very nearly follows him. Kwan was played by Tim Lounibos.