Kim is portrayed by Garrett Wang.
Although Kim is present aboard Voyager throughout the entire series, he actually does die in the Season 2 episode "Deadlock". In the first half of the episode, Voyager is struck by a series of spontaneous proton bursts that cause tremendous damage to the ship. A hull rupture occurs on Deck 15 while Kim and B'Elanna Torres are trying to stabilize the draining anti-matter supply and the decrompression throws Kim out into space, killing him instantly.
However, it is later revealed that Voyager ran afoul of a spacial scission phenomenon. This resulted in the existence of two duplicate Voyagers existing in the same point in spacetime, whose crews were initially unaware of each other due to both ships existing slightly out of phase with each other. Because the antimatter in Voyager's warp core was not duplicated, both ships experienced what they believed to be an unexplained drain on their antimatter supply, as both ships shared the same source of energy. Both crews came up with the idea of infusing the warp core with repeated proton bursts to keep their engines running. However, one Voyager began emitting the bursts before the other, causing serious damage to the other ship which led to Harry Kim's death.
The two Voyager crews eventually became aware of each other's existence through a spatial rift which linked the two ships. They initially attempted to merge the two ships by recreating the divergence field and then depolarizing it by emitting a massive resonance pulse from their deflector dishes. The attempt failed, however, when the ships were thrown further out of phase with one another.
One of the Voyagers found itself under attack by the Vidiians, but the other ship was out of phase and so went unnoticed by the aggressors. Deciding to destroy her ship to save the other Voyager, the Captain Janeway of that ship set hers to self-destruct, and sent her ship's Harry Kim and the newborn Naomi Wildman through the spatial rift to replace their deceased counterparts on the other Voyager.
Since the death of the original Kim, the duplicate Kim has resumed his old life and is regarded as the exact same person as the deceased Kim, since he is essentially the same man from a slightly different timeframe. Although he does not die again throughout the rest of the series, Kim has an incredible run of bad luck and suffers a number of life-threatening incidents.