Science officer of the USS Excelsior under Captain Hikaru Sulu in 2293, who identifies the Praxis shock wave and whose death Tuvok relives in the Voyager episode Flashback.
Dimitri Valtane is played by Jeremy Roberts in Star Trek VI: The Undiscovered Country and again in the 1996 Voyager episode Flashback. In the film he is at the science station when a subspace shock wave hits the Excelsior, and he traces it to the Klingon moon Praxis.
Flashback revisits the same days through the memories of Tuvok, then a young ensign who shared quarters with him. As Sulu takes the ship into the Azure Nebula to help Kirk and McCoy, Kang's battle cruiser attacks, a console explodes and Valtane dies in Tuvok's arms.
A memory virus that had passed from Valtane to Tuvok at that moment disguises itself decades later as a false childhood trauma. Since the film shows Valtane on the bridge in its closing scene, his fate is a well-known continuity puzzle.