William Ryan was a Colonel in the United States Marine Corps and a former commanding officer of Marine Gunnery Sergeant-turned-NCIS Special Agent Leroy Jethro Gibbs.
Col. Ryan is a career marine who has dedicated his life to the Marine Corps and serving his country. He is highly decorated and his participated in multiple overseas operations. He was Gibbs' superior officer when Gibbs was in the service.
NCIS Season 1Edit
Col. Ryan is captured by a secret Black Ops group in Iraq, from whom he escapes with the help of a rescuer. He makes his way back to the United States under an assumed name with the help of a former subordinate, Lt. Cameron. The FBI accuses him of embezzling $2 million and attempting to escape with it, murdering other members of a convoy in the process. He contacts Agent Gibbs and enlists his help in proving his innocence, as well as uncovering the conspiracy that he believes has been using military funds for illegal operations in the Middle East since Operation Desert Storm.
It is revealed at the end of the episode that Colonel Ryan is suffering from paranoid schizophrenia, and has imagined both the conspiracy and the return of Lt. Cameron, who died many years ago under his command; though he does successfully uncover an embezzlement scheme. He is placed in treatment for his mental illness.