Blackguard was among the insults which the Sixth Doctor applied to Astrolabus. (COMIC: Once Upon a Time-Lord)
The Second Doctor described Grey as a blackguard. (TV: The Highlanders)
The Fourth Doctor noted to George Litefoot that a murderer of young London women, later found to be Magnus Greel, was a blackguard. (TV: The Talons of Weng-Chiang)
Redvers Fenn-Cooper described Josiah Samuel Smith as a blackguard. (TV: Ghost Light)
Friar Tuck described the Twelfth Doctor as a "skinny blackguard". (TV: Robot of Sherwood)