Captain Miller is the United States Army officer Chakotay believes himself to be in the Hirogen's Second World War simulation, leading the American advance into Sainte Claire in The Killing Game.
Captain Miller is the identity given to Chakotay in the fourth-season Voyager two-parter The Killing Game. Under Hirogen control, the crew are scattered through a holographic recreation of occupied France and compelled by neural interfaces to live as its characters.
Miller commands the American infantry pushing towards the town of Sainte Claire, where he is to link up with the local Resistance led by Katrine. With him is Lieutenant Bobby Davis, the role assigned to Tom Paris.
When the holodeck walls are breached and the simulation spills through Voyager's decks, Miller's soldiers end up fighting holographic German troops in the ship's corridors. Chakotay stays in character until the interfaces are disabled, after which those same holograms help the crew against the Hirogen.