The exact etymology of this term for a villain is uncertain. What is known is that it is literally from black guard; it is English in origin; and it dates to at least 1532. The earliest known use of the term is from that year and appears in an account book from St. Margaret’s church in Westminster:
Item Receyvid for the lycens of iiij. torchis of the blake garde vjd.
It is not know what or who the black guard referenced in this quote was. They could have been black-uniformed guards or perhaps funerary torch bearers.
By 1535, blackguard was being used to refer to the lowest servants in a household and by 1560, it was being used to refer to attendents, dressed in black and often attending some villainous character.
The Oxford English Dictionary doesn’t dismiss the possibility that there may literally have been a company of soldiers at Westminster called the Black Guard, but no direct evidence of this exists.
The sense of the vagabond or criminal class doesn’t appear until the 1680s. And the modern sense of a scoundrel dates to the 1730s.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton