Briar Cudgeon's background is not talked about much in any of the books, but it is said that his family was politically powerful. In Artemis Fowl, he is a power-hungry lieutenant in LEPrecon and is jealous of Commander Root's position. It also says that he used to be Commander Root's roommate. They even grew up in the same tunnel, and knew each other for over 600 years. He is one of the few people to call the commander by his first name.
At first, he just gives the impression of being a pompous but essentially harmless individual. However, his true sinister nature soon emerges. He is Retrieval One's leader, then he becomes Acting Commander during the Artemis Fowl Siege. After an attempt to exploit the situation and seize power, his plan is thwarted, and in a rage he chokes Foaly. Root incapacitates him with a tranquilizer dart. The dart makes Cudgeon deformed by reacting with some banned mind-accelerating drugs that he had been experimenting with. He is demoted to the rank of private and was left consumed with a desire for vengeance. He joins forces with Opal Koboi in the Arctic Incident and, together, they began a plan to take over The Lower Elements by supplying the B'wa Kell with weapons.
However, he planned to kill the goblins as well as his partner, when they were of no further use. In a complex turn of events, Briar's schemes are revealed to Koboi by Artemis Fowl and Foaly. Koboi flies into a rage and assaults Cudgeon who, in the ensuing struggle, is thrown into the plasma supply for the DNA cannons at Koboi Labs and killed. Ironically, it was he who activated the plasma cannons.