Justified: Emperor Evulz has terminal cancer, and General Drake was simply the most capable candidate to carry out his will.
Or Emperor Evulz and General Drake are friends, and Drake doesn't mind doing the fighting. Or Drake is a mercenary hired just for that purpose. Or Drake believes in Evulz' cause, and volunteers for the job. Etc, etc. This is an easy one to justify, folks.
Enforced: "We need to stall for time before the heroes face the Ultimate Bad Guy. Let's write this guy in."
Lampshaded: "Say hello to General Drake of the Seven Swords. If you expect to meet me in combat, you must face him."
Invoked: Emperor Evulz decides to promote the toughest Mook he can find to Curb-Stomp Battle our heroes and help him stall for time to activate his sinister scheme.
Defied: General Drake's attempt to block our heroes is thwarted when he's brutally tossed off a bridge.
Discussed: "Wait. Our trek here was too easy. Isn't this where someone nasty comes before us?"
Conversed: "I've noticed a lot of villains have this one guy that does their dirty work."