Damon Werth is a former Corporal in the United States Marine Corps and also a former mercenary associated with First Defense Incorporated, the largest private security firm in the United States.
Born in Michigan, Damon Werth came from a military family, and his lifelong dream was to be a United States Marine. Unfortunately, when he initially applied to the Corps at age 19, he was diagnosed with an anemic blood disorder that led to him being rejected. Desperate, he obtained steroids and other drugs that masked their presence, successfully improving his blood count and securing his enlistment in the Corps three years later, at age 22. Thanks to a combination of the steroids and his own determination, he scored outstanding marks in boot camp, and glowing reviews from every C.O. in every assignment he was given. A "Marine's Marine", he devoted his entire life to the Corps - the only "vacation" he ever took was to England, running an advanced tactical course with the British Army's elite Special Air Service commandos.
As a Corporal, while on deployment in Iraq, his squad was captured and tortured. Werth broke free, killed their captors with his bare hands, and single-handed carried his squad mates across the desert to safety, an act for which he was cited to be awarded a Silver Star.
NCIS Season 5
Werth first appeared in "Corporal Punishment", being treated in a psychiatric ward at Bethesda Naval Hospital after returning from Iraq. He was believed to be suffering from Post-Traumatic Stress Disorder, but in fact he had undergone a psychotic break as a result of his prolonged steroid use. Believing that he was still being held prisoner in Iraq, he broke out of Bethesda, kidnapping his physician, Dr. Adrian De La Casa and "infiltrated" a rehabilitation facility where one of his squad mates was being fitted for a prosthetic leg.
The NCIS Major Case Response Team apprehended him there, but not before he had inflicted serious injuries on nearly all of the team.
Realizing that Werth's psychosis was something more serious than PTSD, Leroy Jethro Gibbs's team first theorized that Werth had been the subject of an experimental "super-soldier" program. When they visited Werth in the hospital, he almost overdosed on a sedative, that a hospital orderly had deliberately injected to kill him. The orderly revealed that he was simply the latest in a long line of drug suppliers that Werth had used to obtain his steroids and masking agents.
Knowing that the rest of his squad mates would be under suspicion of supplying him with the drugs unless he confessed, Werth did. He was dishonorably discharged from the Marine Corps, and his Silver Star citation was canceled. But in recognition of Werth's devotion to the Corps and his indisputable heroism, Gibbs gave him a Silver Star that Gibbs himself had received while in the Corps.
During this ordeal, Werth developed a close bond with Ziva David, first as the only member of the team that managed to subdue him during the fight at the rehabilitation center, and later as a calming influence that helped him ease out of his latest psychotic episode without hurting anyone or needing to be shot.
NCIS Season 7
Werth later appeared in "Outlaws and In-Laws", having joined First Defense, Inc., the largest private military company in the U.S., under the direction of former Army Colonel Merton Bell. His last mission for the company was to "rescue" Leyla and Amira Shakarji from the home of their "kidnapper," Mike Franks. His team stormed into the house where they were supposedly being held, but he was shocked to recognize Ziva, and even more shocked to be told that the home belonged to Gibbs, and his team was in effect abducting an innocent woman and her daughter. He immediately turned on his fellow mercenaries, knocking them unconscious. He told Bell he was resigning his position with First Defense, and testified to Bell's actions that led to Bell being arrested and extradited to Mexico for illegal bounty hunting.
Werth's final appearance was in "Jack-Knife". He had been drugged after a troubling conversation with another former squad mate, Nick Heatherton, who was found murdered the next morning. He agreed to participate in a "sting" to catch the suspected killer, Aaron Szwed, which involved riding with Ziva on a cross-country truck route, and helping Szwed to hijack a shipment. Szwed was arrested, but found to be innocent of Heatherton's murder. After the real killer was exposed, Werth planned to travel to Cleveland, Ohio to inform Heatherton's ex-wife and daughter of his death. Anthony DiNozzo, who had gone to college at Ohio State, offered to call some friends of his in the Columbus area to help Werth find a job, an offer Werth accepted gratefully. He also told Ziva that he would "see her later", making DiNozzo press her for specifics, which she refused to give.