Template:Infobox Lost character Desmond David Hume is a fictional character on the ABC television series Lost portrayed by Henry Ian Cusick. Desmond was not a passenger of Flight 815. He had been stranded on the island three years prior to the crash as the result of a shipwreck.

Desmond attended university, but failed to graduate due to his support being needed by his three brothers when their father left them. He also worked as a set designer for the Royal Shakespeare Company. Desmond was engaged to a woman named Ruth for six years. One week before the wedding, Desmond got cold feet and passed out due to binge-drinking. He woke up to find a monk named Brother Campbell, and Desmond decided to join the monastery, feeling a higher calling. While labeling wine bottles one day, Desmond is assaulted by Ruth's brother, prompting him to pay her a visit. He explains to her about his higher calling, but she angrily calls him a coward for jilting her. That night, Desmond breaks into the wine cellar and starts drinking when he is dismissed by Brother Campbell. He offers him to catch a ride into town with Penny, who delivers the wine for them. Two years after meeting, the two decide to move into an apartment together.

Desmond visits Penny's father, Charles, at his office in an attempt to ask his daughter's hand in marriage. While Charles apprehends his bold gesture, he disapproves of Desmond, saying he is not good enough for her. Demond comes to realize this when he is unable to pay for a photograph, and breaks up with her. In an attempt to prove himself to Charles, Desmond joins the Royal Scots Regiment of the British Army, only to become dishonorably discharged when he refuses to follow orders. He also serves time in prison, and upon being released was presented with his belongings, one of which is the book Our Mutual Friend. He is greeted by Charles, who admits to confiscating his letters sent to Penny, and pays him off to leave her alone. Desmond travels to America, where he meets Libby. She gives him her boat when he reveals his plan to win a boating race, funded by Charles Widmore.

Before setting off, Desmond trains at a stadium, where he encounters Jack. He offers some encouragement before resuming his training. Upon leaving, he is confronted by Penny, who is upset about him not contacting her. Desmond asks her to wait for him for one more year, when the race will have ended. As he enters the race, his boat (the Elizabeth) is caught in a ferocious storm, and is eventually knocked unconscious.

Sometime in 2001, Desmond washes ashore on the island without his boat. A man named Kelvin Joe Inman emerges from the jungle in a HAZMAT suit and takes him back to the hatch. He asks if Desmond is "him" and is upset when he realizes that he is not. Desmond watches as Kelvin inputs the numbers into a computer. When Desmond asked, "What was all that about?" Kelvin responded, "Just saving the world." He tells Desmond to inoculate himself with an unnamed vaccine every nine days, since he was out in the "quarantined" island, and may be infected.

Kelvin trains Desmond about the operations of the hatch, including the button (which he explains safely discharges an unusually strong magnetic fluctuation situated beneath them) and ways to trigger a lockdown. Desmond also witnesses Kelvin painting the blacklight picture on the bulkhead doors, which was started by Kelvin's old partner, Radzinsky. Desmond asks what happened to him. Kelvin points to a stain on the ceiling, explaining it is all that is left of Radzinsky, as this is the spot where he took his own life.

Three years pass, and Desmond desperately wants to go above ground, but Kelvin never allows it, although he himself leaves for hours each day in his HAZMAT suit.

Desmond catches Kelvin drunk one night in a secret crawlspace below the floor, dangling a key above a fail-safe mechanism. Kelvin explains that if the fail-safe mechanism is activated, the hatch will be destroyed, destroying the electromagnetic fluctuation beneath them.

When Kelvin leaves one day, Desmond notices that Kelvin's HAZMAT suit has a tear on its leg. He follows Kelvin above ground, where he discovers Kelvin removing the suit and finds the air is safe to breathe. Desmond follows him to a cove, where he sees his sailboat in perfect shape. Kelvin had been leaving the hatch to fix the boat a little each day, planning to escape the island and leave Desmond behind. Kelvin startles Desmond and tells him that he knew he was being followed, and then invites Desmond to escape with him, but Desmond is worried about the button. After Kelvin expresses his doubts about the validity of the button, Desmond becomes enraged that he may have spent three years of his life on the island unnecessarily and attacks Kelvin. They struggle, and Desmond accidentally smashes Kelvin's head on a rock, killing him. Desmond takes the key for the fail-safe mechanism from around Kelvin's neck and races back to the hatch, where the timer has recently reached zero and the computer is registering a system failure. A massive magnetic field builds up, attracting all metal objects to the sealed door inside the hatch, including Oceanic Flight 815, which he discovers later. Desmond manages to stop it by inputting the code, which turns off the magnetic field. However, the plane has crashed onto the island.

For forty-one days, Desmond lingers in the hatch. He gradually falls into a deep depression to the point of even contemplating his own suicide. As he opens up Our Mutual Friend, it being the last book he plans to read, he finds a note that Penny had hidden inside, telling him not to despair, as well as reminding him that she will always wait for him and that she loves him. Even more depressed now, he goes into a rage and makes a mess out of the hatch. As he collapses, Desmond then hears someone shouting from the top of the hatch. Unknown to Desmond, it is Locke asking the hatch for help after Boone's fatal plane injury. When Desmond turns on a light to see who it is, Locke, thinking his prayers have been answered, quiets down. Desmond, similarly, considers the voice to be a sign that he is no longer alone, and regains hope.

When Locke, Kate and Jack enter the hatch, they accidentally damage the computer after a brief firefight with a panicked Desmond. Convinced that the world is going to end, Desmond frantically flees the hatch. Jack catches up with him; Desmond tells him the code, and to enter it every 108 minutes. He then recognizes Jack from their encounter at the stadium, and he asks him about the patient he had mentioned operating on. Desmond leaves saying, "See you in another life, yeah?" as he had in their first encounter. Although it was not shown exactly how, Desmond manages his way back to the Elizabeth and attempts to sail to Fiji. However, his plans go awry.

A drunken Desmond returns in his boat, having been unable to navigate away from the island, making him compare it and its waters to "a bloody snow globe." Later he is confronted by Locke who tells him of the station 5 (The Pearl) orientation film he and Eko saw, and Desmond begins to lose his faith in the button. While Desmond wavers back and forth with his conviction on the button, he and Locke trigger another lockdown, trapping Mr. Eko outside the computer room, and they wait for the countdown to hit zero, to see what will happen. Eko uses dynamite from the Black Rock to attempt to get back into the computer room, but he fails.

As the countdown reaches zero, Locke shows the printout he obtained from The Pearl. Desmond realizes that the date of the prior "system failure" was the same day as the plane crash, September 22, 2004. Desmond believes that his failure to push the button that day resulted in a magnetic field that pulled down Oceanic Flight 815. He is insistent that the button must be pressed, but Locke angrily reacts by destroying the computer. Desmond retrieves the key to the fail-safe mechanism, wanting to save Locke because Locke saved him the night he shouted at the hatch door. As Desmond uses the key, a bright white light envelops his face.

Upon turning the key, Desmond is sent back to 1996, where he relives the moments leading to him leaving Penny. He remembers the island only after seeing Charlie busking in the streets. He is told by a woman, Mrs. Hawking, that it is his destiny to be on the island. When Desmond snaps back to the present, he finds himself amidst the hatch's scattered remains, completely naked. Hurley clothes him, and Desmond tells him of Locke's speech, which is yet to occur. Upon returning to the beach, he then asks Claire to leave her shelter for the day. When she refuses, Desmond constructs a lightning rod, diverting the ensuing lightning to strike it instead of her shelter. Desmond accompanies Locke, Sayid, Nikki and Paulo to the Pearl station, where they witness a live surveillance from inside the Flame station. He leaves, moments before Eko's death. After his burial, Desmond informs Charlie and Hurley in the jungle, but leaves suddenly to rescue a drowning Claire in the ocean. In an attempt to question his clairvoyant gift, Charlie and Hurley get him drunk, but Desmond retaliates before being interrogated. He later informs Charlie of his impending death.

Desmond constantly reminds the two that he cannot simply experience visions by will, particularly when Charlie wishes to know about his demise, and also when Hurley asks him to help in the investigation of the apparent deaths of Nikki and Paulo. He does, however, inform Hurley of an argument between Nikki and Sawyer earlier that morning. The next morning, Desmond experiences more visions, and asks Charlie, Hurley and Jin to accompany him on a hike to the cable in the sand. That night, the four witness a passing helicopter, and its pilot bailing at the last minute. They trek inland, discovering various belongings of the pilot, including the photograph that Desmond and Penny took together, prompting him to believe that the pilot is actually his former fiancée. Desmond rescues Charlie from a foreseen death, which he failed to mention earlier. The four eventually find the parachutist suspended from a tree. Desmond cuts her down and removes her helmet. However, he is disappointed to find that it isn't Penny after all. She coughs out his name before passing out. When Mikhail arrives, Desmond bargains with him to help her in exchange for his freedom, having captured him. He agrees, and manages to tend to her. The four return her to the beach soon after.

Desmond suggests informing someone about Naomi's arrival, and approves of Charlie's decision to tell Sayid over Jack. He tells Sayid about Naomi's mission to find him for Penny. The next day, as Jack and Juliet lead the camp into the jungle, Desmond experiences more visions of Charlie's death, but will ensure the rescue of Claire. He tells Charlie, prompting him to sign up for entering the Looking Glass station. Desmond accompanies him, and follows the cable into the ocean. Desmond offers to take his place, thinking that Desmond is supposed to be dying in Charlie's place, but is knocked out. Desmond comes to, only for Mikhail to shoot at him. Desmond swims down to the station and hides in a locker. He shoots Mikhail after he kills the two resident Others, but is confused when he is unable to find his body minutes later. Charlie makes contact with Penny, and informs Desmond, but before he can enter the room, Charlie shuts him out. Desmond watches helplessly as Mikhail blows open the window, causing Charlie to eventually drown. Moments before drowning, Charlie informs Desmond that Penny is not on Naomi's boat.

In keeping with the shows motif of naming important characters after important philosophers (e.g., John Locke, Jean-Jacques Rousseau and Mikhail Bakunin), Desmond David Hume is named after the famous Scottish Enlightenment philosopher, economist, and historian David Hume.