From Longman Dictionary of Contemporary Englishblackguardblack‧guard /ˈblæɡɑːd, -əd $ -ərd, -ɑːrd/ noun [countable] old use BAD PERSONa man who treats other people very badly
Examples from the Corpus
blackguard• McQuaid was a drunken blackguard who was with me in the war.Origin blackguard (1700-1800) black guard “soldier of bad character” ((16-18 centuries)) 