Ben Corbin is an agent for the CIA.
Corbin was the son of a strict missionary who chose to bring Christianity to the Korean "heathens". After Corbin fell in love with a Korean girl, though, he was sent back to America to attend divinity school. Rebelling, he joined the American Army instead and, during the Second World War, served in the European theater. Back in Korea, his parents died beneath the swords of the invading Japanese.
Returning home after the war, Corbin is there to take part in the Korean War, both as an American sergeant and as a citizen of the Republic of Korea. He is allowed to create a private army with the title of the Invader Security Force with the instruction to fight the fight that the U.N. forces were prohibited in fighting, using techniques that were far from normal.
It was while with this force that Corbin again met the beautiful Ajah and with the parents on both sides now gone, the two are married. This marriage also sealed Corbin's attachment to his homeland and set the scene for his service to both the CIA and the ROK Secret Service.
Corbin is driven by two major compulsions; his love of Korea and his very mixed feelings about his father.
The affiliation with the country of his birth is incredibly strong in the first two books and then lessens with the remaining books, possibly because of what transpires with his wife.
The fixation on his father never changes. In virtually every major event that might trigger an emotional response, that response comes with remembrance of something his father said or did. It is always with a passage from the Bible Corbin was forced to memorize and frequently with the recollection of a beating.
As the stories go on, the focus of his fixations change to a matter of revenge but the intensity never wavers.
The last book in the series really does not belong with the others even though it is the same character. With apparently a new publisher, Crane brings back Ben Corbin after a 13 year hiatus by taking the case found in Operation Vengeance, dusting it off, and retelling it. The dusting-off certainly results in some major cleaning, however. Suddenly, Corbin's father was a missionary to Japan instead of Korea. Corbin was born and raised in Japan, not Korea. His allegiance is to the U.S., not to Korea. His time in the military is spent in Vietnam in the mid 60's, not Korea in the early 50's. Other than those small items, it is the same story with the same characters. The writing style is faster, the action harder, and the women more lustful.