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"What is thy bidding, my master?"

"This world and everything in it now belong to darkness! They belong to my master!"

— Ghirahim, The Legend of Zelda: Skyward Sword

There is almost always someone, person or monster, The Hero has to get past to get at the Big Bad. Much of the time, but not necessarily, this is the Big Bad's top enforcer. He, she or it embodies a narrative trope: the penultimate challenge that the hero must face before confronting the Big Bad. This challenge will test their worthiness in some fundamental way.

Some Dragons are ferocious fighters who leave the heavy thinking to the boss. Others are smart, detail-oriented administrators who oversee the day-to-day running of the evil organization. A common but by no means universal theme is to have the Dragon pose a physical challenge to the hero, while the Big Bad poses a mental or moral challenge.

This role is somebody the Big Bad can rely on (or thinks they can rely on) in a time of trouble to step up and beat the living heck out of The Hero, or maybe just take charge for a while, should the Big Bad not be around to do the job.

The term dragon for this role originates from analysis of folklore in which the hero fights dragons or other monsters. As described in "The Hero with a Thousand Faces", a non-fiction comparison of various fantasy heroes written by Joseph Campbell, monsters serve as obstacles to be overcome in order to fulfill the hero's quest. Note, however, that in folklore they are villains or obstacles in their own right (see the tale of Saint George The Dragonslayer) whereas in accordance with this trope (which mostly applies to modern media) they are often subordinate to other villains.

For literal dragons and their permutations, see Our Dragons Are Different. Not to be confused with Dragon Lady, who is more likely to be a Big Bad than the Dragon, or Dragon, which was a magazine. Definitely not to be confused with The Savage Dragon.

Beta Bitch - Number Two to the Alpha Bitch, often fills the Dragon role when the Alpha Bitch is the Big Bad.
Co-Dragons - Two or more characters split the Dragon role between them.
The Creon - A Dragon is this if they vehemently rejects every opportunity to become the Big Bad.
Demoted to Dragon - A previous Big Bad is revealed to be, or is reduced to being, the Dragon to another villain.
Devour the Dragon - The Big Bad kills the Dragon in order to become stronger.
Dragon Ascendant - When they take over from the Big Bad after the latter is defeated or leaves.
Dragon-in-Chief - When they are more dangerous than the Big Bad and the de facto main villain of the story. Like Dragon with an Agenda, may be The Man in Front of the Man. Not to be confused with The Heavy.
Dragon Their Feet - When the Big Bad is defeated or killed first. The Dragon may or may not show up afterwards to rescue or avenge them, but they might just take their business elsewhere.
Dragon with an Agenda - When they have different goals from the Big Bad. If those goals are mutually exclusive, The Starscream, Rule of Two or Dragon-in-Chief may be in play.
The Heavy - The "active" villain that drives most of the plot. This is more often the Dragon than the Big Bad, since most authors want to keep the Big Bad in the background and mysterious for most of the story. Not to be confused with Dragon-in-Chief.
It's Personal with the Dragon - When the Dragon is the hero's Arch-Enemy instead of the Big Bad.
The Lancer - The Good Counterpart in the Five-Man Band.
Mook Lieutenant - When the Dragon is merely the leader of the Big Bad's minions when the Big Bad isn't around.
Mouth of Sauron - When the Big Bad themselves is almost never seen taking an active role, The Dragon is usually the one who picks up the slack on reminding people why they're afraid of the Big Bad in the first place.
Noble Top Enforcer - A trope that often overlaps with the Dragon; when the Big Bad's Number Two is an Anti-Villain that is considerably more virtuous than their master. Likely to turn on the Big Bad if their actions piss them off enough.
Number Two - The second-in-command of a team or organization, often overlapping with The Dragon.
Number Two for Brains - A bumbling Dragon.
Rule of Two - A standard Big Bad and Dragon dynamic where betrayal is expected, and often inevitable.
The Starscream - A traitorous Number Two; often fulfills the role of the Dragon.
Villainous Friendship - When a Dragon is good friends with the Big Bad.