Ian Sykes was a former Special Forces Green Beret in the U.S. Army. After leaving the Army, he sold his talents as a professional mercenary and assassin.
In 2002, he was hired by Gavin Lloyd to eliminate two potential witnesses to Lloyd's crooked dealings: Nicole Vasques and Jason Ronstadt, both associated with mayoral candidate Warren St. Claire. Sykes performed both murders, stabbing Vasques in her home and shooting Ronstadt with a sniper rifle during a political rally. Ronstadt's murder was meant to be seen as a failed assassination attempt on St. Claire - according to Lloyd's plan, it would both camoflage the real motive for Ronstadt's death, and boost St. Claire's popularity in the upcoming election.
Shortly afterwards, Gavin Lloyd hired him again to eliminate a Volunteer worker named Jake upon discovering that he managed to find a connection between Nicole Vasques and the election campaign volunteer workers. Sykes managed to do so by posing as a beggar who washes cars for money (much to Jake's dismay due to the fact that he already had the car cleaned), and then killing him by smashing his head against the steering wheel as soon as he opened his window to offer him change, and then make it seem like he was killed in an awry accident in regards to driving too fast and falling down the edge of a hill.
Sykes's most distinctive feature was his imposing height of 6'5, which Adrian Monk deduced from clues left at both murder scenes. When the SFPD, with the help of the F.B.I., traced the rifle used in the shooting to Sykes, he cleverly pretended to be disabled, bound to a wheelchair and thus unable to have shot anyone. But as soon as the police left his apartment, he stood up from the chair and fled, anticipating that the SFPD might catch on sooner or later (a suspicion confirmed when Monk pointed out to Stottlemeyer that Sykes had scuffles on his shoes, something that a person truly bound to a wheelchair could not have). Monk almost cornered him climbing down a ladder from a rooftop, but the detective's crippling fear of heights allowed Sykes to ease past him and make a getaway.
The next day, it is revealed that he stayed in San Francisco instead of fleeing the country. During a recreation of the original shooting, he shot Lloyd in the arm with his rifle out of what Monk called a "contract dispute". Sykes then tried to escape by means of the sewers. He was followed by Sharona Fleming, who he took hostage. He was cornered at the end of a sewer tunnel by Adrian Monk, who shot him with a "borrowed" handgun. Receiving a glancing blow to the side of his head, Sykes survived and was taken into custody.
Sykes was tried and convicted for the murders of Vasques and Ronstadt, and was sentenced to life imprisonment.
Sykes smoked menthol Newport cigarettes.
In a deleted scene, Sykes was summoned to the pier by Gavin Lloyd due to something of utter importance. Lloyd then arrived at the rendezvous point, and when asking him what was so important that needed him to come to the docks, he then found himself with Lloyd pointing a pistol at him and is shot.