We've previously touched on Sauron, Morgoth's understudy-turned-successor in cosmic-level unpleasantness, but the original Lucifer-figure of Tolkien's fictional mythology is vivid enough as a study in morbid fantasy totalitarianism to earn his own spot in the pantheon of Great Bastards. While Sauron's story is the tale of his rise from rebel spirit and manipulative shape-shifter to all-powerful god-king, Morgoth's is of a long and miserable descent, through boundless humiliation and destructive rage, from a god-like being with pretensions to trademark the very matter of creation down to a mere despot who sacks civilizations out of frustrated spite; mighty yet wretched in the hollowness of his glory.
The consistency and attention to detail with which Tolkien handled the guiding themes of his invented universe really helps to keep Morgoth and his followers in Evil a compelling a threatening presence, hovering grimly over the long and glorious history of Middle Earth. Morgoth is the original model for the basic nature of evil as imagined by Tolkien; arrogant rebellion against a natural order in the name of jealousy and ego. From before the very beginning of time, according to the Silmarillion, Morgoth, formerly known as Melkor, nursed an insane, impossible ambition to nab the credit for the creation of the cosmos from Iluvatar, Tolkien's actual creator-God figure. Instead of collaborating with the other Valar (an order of archangel stand-ins sent by Iluvatar to mould the young Earth according to his intent) Morgoth tries to wrestle the divine plan into a new shape, turning the world into his personal empire and temple to his sole glory. This rampant megalomania only ends of perverting and corrupting the world, supposedly causing everything harsh and dangerous in the environment; Melkor's evil is so primal that he's ultimately responsible for natural disasters!
All the malevolent forces that confront chirpy Hobbits, even thousands of years after Morgoth's defeat, are the sad, twisted end-results of his attempts to imitate Iluvatar's ineffable ability to create life; trying to breed new species that exist to serve him as slaves and soliders, the would-be world-shaper only ends up fashioning violent monsters. In every single mention of him in Tolkien's writings, he seems to be poisoning or wrecking something, so given over to vengeful hostility and an almost mindless power-lust that he ends up earning his suitably sinister name for acts of murder and treachery; Morgoth, "Dark Foe of the World", a being so violent and cruel that it's effectively locked in battle with the entire planet at once, apart from pawns that follow him out of fear and shared hatred of anything beautiful.
The most noteworthy thing about Morgoth is how his immense power relative to his Elven enemies in the Silmarillion never stops him from seeming contemptible and somehow pathetic, because his motives are so crude and his egotistical obsession with talking himself up as the Supreme Master of Everything so clearly desperate and forced. He might eventually overrun most of the continent and end up victorious everywhere, but the Elves, lesser creatures supposedly beneath his notice, undeniably give him a run for his money before their kingdoms are smashed, and he even demonstrates the very un-godlike emotion of fear when the Elf King Fingolfin actually dares to challenge him to a duel and comes close to winning (directly inspiring an awesome power metal song by Blind Guardian countless ages later).
Morgoth is ultimately flattened by his former colleagues the Valar, when they are persuaded into a one-time-only intervention that reduces the Dark Lord's vaunted empire to flaming rubble. They find a ranting, hideous shell of a being, whose military power and sinister trappings managed to disguise the fact that he had literally wasted away on a diet of Evil, pouring his essence into the world to try and control it but only succeeding in tainting it with his bottomless hatred.
In fairness, if a Dark Lord is going to exit the scene in style, being wrapped in an unbreakable chain and shoved through a door in the edge of the universe to fall through empty space forever is a suitably epic fate that any self-respecting Dark Lord would be happy with. Still, perhaps the transformation of Morgoth's infamous "look" into the most easily-mocked cliche of popular fantasy is the suitable final humiliation for the overgrown thug?