In the Age of Apocalypse, Apocalypse's Omnicidal Maniac son Holocaust was the most devoted to him among his Four Horsemen, and in turn enjoyed the most favor among them (though even he had designs on supplanting his father and turning the world into a hellscape (well, even more of a hellscape) in which no one would be fit to survive.)
In Avengers Under Siege, Baron Zemo used brainwashing to turn the monstrously powerful (but mentally unstable) Blackout into his loyal Dragon. Blackout is interesting in that he defended Zemo from heroes and villains alike: he disabled the Avengers' most powerful member, Captain Marvel, and also prevented dissent among Zemo's Masters of Evil. Tellingly, Moonstone, in her role as The Starscream, spent the entire arc trying to win over Blackout rather than trying to kill Zemo.
The Batman villain Ra's Al-Ghul is usually accompanied by an extremely large thug named Ubu. Apparently this is a title, rather than a name; he tends to replace Ubus fairly frequently. Ubu was absent from the film, but Ken Watanabe's fake Ra's could be said to fulfill this function.
In the limited Superman, Batman and Wonder Woman series Trinity (the three issue Matt Wagner one, not the more recent 52 issue maxiseries), Ubu is present, but the role of Ra's Dragon falls to Bizarro, and the mysterious Amazon Artemis of Bana-Mighdall
In the second adventure The Mystery of the Great Pyramid, Olrik gets his own dragon: Sharkey.
In Bone, both Kingdok and The Hooded One have claims to the Dragon position. It could even be argued that Kingdok was the Dragon for the Hooded One.
Captain America villain Crossbones would be The Dragon to the Red Skull's Big Bad. The merc Crossbones is a deadly physical threat, a skilled fighter and carries out the fisticuffs for the weaker (most of the time) but far more cunning Skull.
His daughter Sin has acted as the Dragon on occasion as well, and of the two of them, she's the one who's become the Dragon Ascendant. Crossbones doesn't mind through, since he gets to form an evil Battle Couple with her.
In Legacy, Darth Krayt has many elite minions who act in the enforcer role, but the one who is closest to him and who he relies on completely is Darth Wyyrlok. In addition to being the only being in the galaxy Krayt can be said to really trust, Wyyrlok is also potentially more powerful than his master, as Krayt has been weakened by Yuuzhan Vong parasites. Ultimately, Wyyrlok subverts this trope in an interesting way- he remains absolutely devoted to Krayt's vision of a galaxy united under the Sith, but kills the Dark Lord anyway because he believes his master has gone insane and lost track of his true goals.
Even if she is usually not privy to his plans, Mazikeen is Lucifer's most trusted servant, and often fills this position.
In Matt Wagner's Mage: The Hero Discovered, Crom Cruich is both a literal AND figurative dragon, summoned by the Umbra Sprite as an "ultimate Enforcer."
Magneto from the X-Men has employed a number of Dragons over the years. The first was Toad, a Sycophantic Servant type who eventually succumbed to the temptation of The Dog Bites Back and betrayed Magneto. After a long stint of working alone and a failed attempt to reform, Mags acquired a new Dragon in the 1991 X-Men relaunch, Fabian Cortez. Unfortunately for him, Cortez was a Deceptive Disciple and betrayed him so quickly it would have made Toad's head spin. Mags got the last laugh though, as after a stint of being believed dead he returned in Fatal Attractions with his strongest and most loyal Dragon, Exodus, who eventually drifted out of the Master of Magnetism's good graces. After an even longer period of working alone, Mystique found herself promoted to the role due to Adaptation Displacement (she's been Magneto's Dragon in most adaptations, though she never even worked with him until recent years). As of 2018 Mystique is the only one of Mags's Dragons who is still in good standing with him.
Qztr and all the other Lawbringers are Charon's Dragons in Negation. Immensely powerful and willing to kill without mercy at Charon's command, they also (Qztr does, at least) act as a court of final appeals within the empire.
Norman Osborn of Spider-Man fame has had several Dragons over the past few years. When he formed the Sinister Twelve, Venom served as his Dragon. When Osborn became head of the Thunderbolts, he brought Venom along for the ride, but would also use Bullseye as his Dragon for more subtle work. Finally, when he formed the Dark Avengers, Venom and Bullseye stuck around, but Osborn now used the Sentry as his Dragon in most cases.
Sin City villains are often this kind of bad guy. Manute, Kevin, Blue Eyes, to a certain extent are all dragons while the Big Bad's like the Roark family and Wallenquist usually work behind the scenes... and thus, a little more likely to survive the story.
In Ultimate Spider-Man, Elektra serves as the Dragon to the Kingpin of Crime. Not that the Kingpin isn't capable of quality violence in his own right...
In the same universe, the Ultimate X-Men have to deal with the Weapon X project, led by a human military officer named John Wraith. He isn't particularly tough, but his personal Dragon is the gigantic mutant killing machine Sabretooth.