Harland Doyle is Jack Carver's main contact on the island Carver was washed up on.
He is an undercover CIA Agent working as a scientist on the island to uncover what sort of work is going on there. Though he is aware of the purpose of Dr. Krieger's unethical experiments, he does not reveal much more of his identity or reasons for being there until later on in the game.
After killing Dr. Krieger in his main facility, Doyle informs Jack Carver and Valerie Constantine that he deceived them and plans to make a fortune off of the acquried mutagen. After this speech, Doyle is now the controller of all trigens (and possibly, the remaining Mercenary forces) that remain on the island.
In Far Cry, Doyle first contacts Jack via a radio left in an old Japanese bunker. At first, Jack is skeptical and does not trust him, but Doyle reassures him by saying that the radio has a bio-reader and that he could have ratted him out by this time if he was against him.
Doyle acts as an instructor and assistant throughout Jack's journey, telling him where and how to locate Val, and giving him heads up about the threats ahead. When Jack eventually rescues Val, he learns from her that she is an associate of Doyle's, and that he is a scientist on the island working undercover for the government.
Upon nuking the Mutagen facility, Jack and Val are captured by Krieger and taken on board a helicopter. Jack is kicked off but survives, and finds another radio next to a helicopter wreck downstream. From there, he resumes contact with Doyle, who tells him Krieger's whereabouts and that Val may be held captive by him. Jack heads to Krieger's office and finds that Krieger has mutated himself. He kills him along with his bodyguards and rescues Val, only to find her in a much more infected state than himself, as the two became contaminated by the Mutagen while in the facility. Doyle appears as a hologram in the middle of Krieger's office, and informs Jack and Val that he has betrayed them. He plans on selling the Mutagen to become rich; using the two all along to do his dirty work (which was killing off Krieger to steal his research and thus ensure the Trigens would not exact their revenge on him). Jack, infuriated at Doyle's betrayal and in need of the antidote, begins to make his way to Doyle's office at the peak of the island's volcano to confront him.
As Carver battles several Trigens and some Elite Guards at the base of the volcano, Doyle frequently radios and taunts him. Upon meeting Doyle for the last time, Carver shouts "Well, this wasn't in plans right?" and promptly shoots Doyle. The wounded Doyle then hysterically tells Jack that through killing him he will achieve nothing, and that he cannot change the future, to which Jack replies - "Probably not, but I can make sure you're not a part of it!" He finishes Doyle off with a shot to the head and retrieves the antidote, later using it to cure himself and Val of the mutagen as they sail away from the island.
Far Cry Instincts
In Far Cry Instincts Doyle's mission is to expose Dr. Krieger's experiments to the government. In the beginning of the game he makes radio contact with Jack telling him of what's going on and he must find Val and escape from Crowe the leader of the militia on the island. He loses communications with Jack after Jack is taken by Crowe and injected with the serum that gives him special abilities. After Jack escapes he makes radio contact with Doyle and tells him what happened. Doyle tells Jack that he must hurry to Doyle saying that there are things Jack must know about the serum and he must have it removed. After directing Jack towards a medical base Jack and Doyle meet with Val in the room and. Doyle starts the surgery on Jack but when Jack wakes up sees enemies he killed but Val and Doyle are gone. Jack meets up with Val and both make it into the communications room finding out that Crowe had gone rogue and took Doyle.. Jack then heads out for Crowe and Doyle and finds Doyle on a base in the wasteland. Doyle tells Jack that Crowe injected himself with the serum but overdosed taking four times what Jack got. Jack and Crowe take an airplane to head to the volcano where Krieger's lair resides but their plane gets hit with a missile. Jack falls out of the helicopter into water but Doyle driving the helicopter crashes. Jack is able to infiltrate the base and is able to kill Crowe and have the surviving abominations turn on Krieger and kill him. Val manages to get a helicopter and extracts Jack moments before the lair explodes. Doyle is on the helicopter with an injured leg and gives Jack a case that contains unknown materials and the Jack is shown opening it and laughing.
Far Cry Instincts: Evolution
In the game Doyle has the responsibility of taking care of the rebels and to find the murderer of a government official. Jack meets him again when Doyle is interrogating Kade and tells Jack his purpose for being in the town. The 3 are attacked by pirates and forced to separate and move to a new location. Jack is able to find Doyle and Kade on top of a tower. Doyle instructs Jack to find a man in a town and to receive some information regarding the assassin. After this Doyle informs Jack that Kade ran off and Jack finds her but she is forced to run. Jack then escapes the town a meets up with Doyle to discuss their next step. Doyle is compromised after Jack heads off and sees him being put into the back of the truck. Jack rides on top of the truck until they reach the base. Doyle runs off and tells Jack to try and sabotage the place. When Jack does this he sees Kade again and tells him that the CIA don't trust in Doyle's ability to solve the issue and bomb the base. The 3 run through an underground area and Jack remains behind to protect them but a soldier with a missile launcher shoots at the elevator and Doyle falls falls into the water being badly injured. Jack gets on a mini boat and get Doyle on it. Doyle tells Jack that there should be an exit and the two make it out. Jack swims Doyle to shore and tells him what injuries he is suffering from, a large group of rebels attack but Jack manages to take them out. Doyle tells Jack to find a vehicle to escape Jack refuses to leave Doyle to die and tells him to hide so he can get the vehicle. When Jack comes back he sees Doyle is missing.he uses his sensing abilities to follow Doyle's blood traces. Jack finds that his signal is being blocked and destroys the signal jammers and finds Doyle's communicator. At Semeru's main base Jack finds Doyle at the steps but Doyle is dead and becomes angry and goes after Semeru. Jack finds Semeru and the two fight but Jack loses and is thrown off the cliff. Jack manages to survives but loses his gear. He finds Semeru again and he tells him that Doyle was weeping before he killed them and called for Jack and he never came. Jack says that even though Doyle was a snake he is more of a man than Semeru will ever be. Jack tries to fight him but once again is overpowered and Jack is betrayed by Kade who stabs him. Jack loses his powers for a short time and engages Semeru in a firefight, Semeru breaks through the wall and the two fight outside. Jack once again able to use his powers finally beats Semeru and kills him by dropping him on a spike. Jack sees Kade and tells him she's sorry and had no choice and Jack instead of killing her gives her the money and opens the gates.