Desmond David Hume was a Scotsman who spent years on the Island. He had a number of unusual experiences there withelectromagnetism, sending his mind repeatedly through time.
Before coming to the Island, Desmond's life seemed to be defined by failure. He was fired as a monk, sadly broke up with his girlfriend Penny Widmore, dishonorably discharged from the Royal Scots Regiment, and regarded with contempt by Penny's father Charles Widmore. In an attempt to regain his honor, Desmond entered Charles Widmore's sailing race around the world and consequently became shipwrecked on the Island.
Desmond spent three years in the Swan station till he discovered his partner Kelvin was secretly planning to escape. He confronted and accidentally killed Kelvin, and his negligence sparked theincident which crashed Oceanic 815. He left the Swan when the Oceanic survivors discovered it, and he joined them after a failed escape attempt as a charismatic, helpful member of the camp. He and Locke tried to test whether the Swan was a hoax, leaving Desmond to turn its fail-safe key to prevent disaster.
The resultant implosion gave Desmond premonitions. He predicted a parachutist's arrival and Charlie's eventual death. He traveled to the parachutist's boat and escaped it after making contact with Penny. He and the Oceanic 6 then encountered Penny's boat, which led them to rescue. Desmond and Penny married and had a son, and they hid from Charles Widmore till a dream convinced Desmond to seek him out. Widmore returned Desmond to the Island, where the Man in Black and Jack both used him to deactivate the Heart of the Island.
After his death, Desmond was the first to recall his life and he embarked on a mission to help his friends remember theirs. Eventually, he succeeded in awakening his friends and, along with them and Penny, moved on.