Nefarious (adjective)
Sinful, villainous, criminal, or wicked, especially when noteworthy or notorious for such characteristics.
“evil|iniquitous|sinister|underhanded|vile|good-for-nothing|Thesaurus:evil”
“Vikings, pirates, outlaws, Native Americans, Confederate soldiers, Roman soldiers, hessians, and German soldiers in both world wars all committed many nefarious deeds.”
“Aliens have a nefarious connotation in many science fiction books.”
Villainous (adjective)
Of, relating to, or appropriate to a villain.
Villainous (adjective)
Wicked, offensive, or reprehensible in nature or behaviour; nefarious.
Wiktionary