Between 1909, when the MI5 was founded (as the Secret Service Bureau) and the present day, there have been 17 Directors General (simply called “Directors” until 1941). Until 1993, the Prime Minister appointed them in secret, and their names and roles were not disclosed to the general public.
The first Director General to be publicly named was Dame Stella Rimington, although the names of several previous DGs had become public knowledge before then.
Since 1993, it has been MI5's policy to name its Directors General. Ken McCallum is the current Director General. In recent years, our Directors General have tended to serve about four to five years in their post.