Drake's background was never explored in detail in the series, and also appeared to undergo an amount of retconning involving his nationality.
In this later version, he works for a fictional British secret service branch called M9; no further reference is made to him being American.
Drake was not opposed to using lethal force when absolutely necessary, however, and on rare occasions did kill villains using other methods (throwing off a train, causing the collision of two airplanes, etc.).
The first season of the 1964–66 series sees Drake receiving orders from Hobbs, a somewhat cold M9 official who is always seen fiddling with a letter opener.
In one episode of the third series, viewers are introduced to a group of M9 technicians who support Drake's missions, including a Q-like gadget man and a wardrobe supervisor.