A member of royal Garrett family, Professor Nathan Garrett was noble englishman who was born in London and a descendant of Sir Percy of Scandia, known in history as the heroic Black Knight of Arthurian legend. Garrett achieved international respect as a brilliant research scientist and inventor whose particular specialty was genetic manipulation. He earned his doctorate at Oxford University and later taught there as a professor. It may have been at Oxford that Garrett fell in with and joined colleagues who were political leftists, and became a radical communist: it is not known at what point in his life, Garrett became a spy for the People's Republic of China.
At some point, Garrett visited his ancestor's castle called Garrett Castle that his father had inherited and the place where his ancestor Sir Percy of Scandia was buried. That was when his father confronted him and presented him with the opportunity to become a modern day Black Knight that would fight against evil. Nathan saw the original Black Knight's Ebony Blade in a scabbard near the tomb of Sir Percy. Believing he was unworthy, Nathan was successful in drawing the sword and his father made Garrett his successor as the Black Knight.
Avengers Civil War
Ever since the destruction of Sokovia between Ultron and the Avengers, Nathan Garrett had become a member of the Avengers, but when he learned of the Sokovia Accords, he refused to register and became a wanted fugitive.