Before the nuclear exchanges that made the world the way it is in the Fallout series, Desmond was a player in international intelligence at the highest levels. Many of his peers and counterparts in high level intelligence knew the inevitability of a nuclear exchange so they tried to find ways of surviving the nuclear hellfire. Most of these people would not use vaults because they knew of the sinister experiments being done by Vault-Tec so they had to find other ways of surviving the coming destruction and chaos. Desmond attempted to administer large amounts of radiation to himself so the radiation from the bombs would not kill him. His plans worked and he became what is likely to be the first ghoul. His ghoulification also had the added benefit of dramatically slowing the aging process, giving him the near immortality that all ghouls possess. After surviving the bombs many of the people who were in high positions before the war attempted to kill their former rivals and counterparts. Desmond seems to wish it weren't this way but he realizes that he has to kill them to stay alive.
The Local Flavor
This quest begins when players install the Point Lookout DLC. Players need to find the way to Point Lookout by way of The Duchess Gambit, which is driven by Tobar the Ferryman. After arriving at Point Lookout, players will have to go to the Calvert Mansion. When they enter they will see Desmond for the first time; he will be fighting Tribals with his dogs Geri and Freki. Help Desmond kill the Tribals and then talk to him. He will tell the player to help him kill the Tribals invading his home. There will be several rooms the player will have to assist Desmond and his dogs clear out. Once players finish sealing the breaches meet Desmond back at the entrance to the mansion for a final assault on the manor. Placing mines will help with the coming fight. After defending the mansion, Desmond will give the player the Superior Defense Perk which adds 5 points to Weapon Damage and 10 points to Damage Resistance when the player is standing still.
Walking With Spirits
After helping Desmond defend his home he will ask the player to infiltrate the Ark and Dove Cathedral, which is the Tribals's settlement, to find out the reason behind the attack. The player has to undergo a ritual and a lobotomy to join the Tribals.
After finding out the location of the Tribal leader's praying ground, where he is commanded by his deity, the player reports back to Desmond. Desmond will tell the player to find the leader in the caves where he worships his god. After fighting through the caves, players will find the leader talking to a holographic brain. After they finish talking talk to the brain. The brain will explain that it is using the Tribals to try to destroy a signal jamming device made by Desmond to stop the brain from being able to broadcast a signal far from its location. Players then head back to Desmond to tell him about this information.
Desmond will then explain that the brain belongs to a man named Professor Calvert, who was a brilliant scientist before the Great War, as well as the only living person in the Calvert family. Before the war Desmond would try to subvert the Calvert family's affairs, one time going so far as to make a scandal involving a presidential nominee and a dog. He will also explain that the Calvert Mansion he has made into a base of operations is the family home of Professor Calvert. They have had a rivalry that is over 200 years old. Desmond will explain that he has a Cogwave Jammer and he needs the player to put it on top of the Ferris Wheel to completely block Calvert's signal.
On the way there Calvert will contact the player and offer an alternative. He will tell the player to put the emitter in the nearby trash compacter. The player now has the choice of whether to follow Desmond's instructions or destroy the emitter. If players side with Desmond they will be attacked by a lot of Tribals and all other unnamed Tribals in their base will become hostile. Upon returning to Desmond's mansion it will explode, leaving only wreckage. Sorting through the wreckage will reveal the entrance to Desmond's panic room, where he will mention how angry he is that his dogs died in the explosion and that he found out where Calvert is. He then tells the player that the feud they have had for over 200 years is about to come to an end.
A Meeting of the Minds
Desmond and the player will make their way to the lighthouse that Calvert has been using as his secret base of operations and find his underground lab. After fighting past Calvert's robotic security, players finally come face to face with Professor Calvert. Players find out that to survive the Great War, Calvert had his brain removed and preserved in a glass tank. From the tank he is able to control all the robots he had produced before the war. Desmond and Calvert will talk before they fight and it is up to the player to decide which side they will support. If players side with Calvert he will promise the greatest thing anyone could ever want (he'll betray the player upon killing Desmond).
If players side with Desmond he will promise any loot of Professor Calvert's he won't need. If players side with Desmond and kill Calvert he will be overjoyed to have finally killed his rival and says that everything Calvert stole from him is now his again. He will give the player a key to a room containing a large amount of loot and a unique weapon called the Microwave Emitter. After everything is done Desmond will say that he is heading north to confront another "player". After Desmond leaves the lighthouse he will no longer be in the game, having left to go north and settle a 200 year old game.
In Fallout: New Vegas
While Desmond was not put in Fallout: New Vegas by Obsidian he has been put in the game by a mod. In the mod the player can either have Desmond join the player as a companion or actually be Desmond Lockheart (in terms of how the character looks anyway). If players want Desmond as a companion then he can be found outside the Old Mormon Fort in Freeside. However he does not have his old voice and uses a standard ghoul voice. The mod can be found here.
Desmond has a very good pair of unique glasses. They have a Weight of 0 and a Damage Resistance of 1. However they also add +5 to the Explosives Skill and +5 to the Small Guns Skill. They are also resilient and have a high item health. They can be repaired with any other pair of regular glasses and Three Dog's Glasses as well Doctor Li's Glasses.
There are several sections of the plot where Desmond is an essential NPC and cannot be killed. When Desmond is killed he will have the following items on his body:
Dirty Pre-War Bussinesswear
2 Combat Shotguns- If they are taken one at a time the other will vanish, the only way to get both is to choose the Take All option.
An Ear- If the player has the Contract Killer Perk then they can loot an ear of his corpse.
Desmond's health and skill points can vary based on the level of the player. Desmond's level is 1.3 times the player's level. His lowest possible level is 5 and he has a level cap of 30. At his weakest he has 335 hit points and at his strongest he has 460 hit points. His Tag Skills are Melee Weapons, Small Guns, and Sneak. By the time Desmond reaches level 30 all of his Tag Skills will be at 100. His SPECIAL stats are: Strength-6, Perception-5, Endurance-4, Charisma-4, Intelligence-4, Agility-6, Luck-4.
"Kid, my story is like a Deathclaw's tongue. It's long, messy and you don't want to get too personal with it."
"Be a good pup, and Ol' Desmond will give you a treat."
"What you betrayed me because I wasn't polite? Are you out of your fucking mind?"
"Then pretty please, fucking help me rid the world of Professor Calvert."
"Those mud-lovers want me dead, and haven't extended the common fucking courtesy to tell me why!"
"So, my hero huh? Think you came in and rescued me right in the nick of time?"
"The type that kills everyone outside of my saferoom and leaves a hell of a mess to clean up. Standard type."
Desmond is voiced by Jeff Baker, who has also voiced Haskill in Elder Scrolls IV: Shivering Isles.
Desmond is the most profane character in Fallout 3, and possibly the Fallout franchise.
At times Desmond has a slight British inflection and a few British affectations when he speaks. Professor Calvert also calls him a "limey" at one point. Based on this it could be assumed that he was an agent for the European Commonwealth.
He is the only ghoul to have both regular hair and facial hair. Raul Tejada from Fallout: New Vegas is the only other ghoul with a mustache and Snowflake is the only ghoul with hair. This could be because of the climate in Point Lookout or the more controlled method he used to administered radiation to himself.
His dogs Freki and Geri are references to the wolf hounds of Odin in Norse mythology.
Desmond is a Good Karma character and considered the Good Karma choice for the struggle between Calvert and Desmond.
It is possible that Mr.House is another one of the "players" in the "Great Game."