Thanos
Iron Man #55 · 1973
He succeeded. Half of everything died, and the story had to spend an entire additional film undoing it.
Danger is a practical measure. It asks how much of the world a villain has already ruined, how hard they are to stop, and what happens if nobody intervenes. A frightening character who kills six people is less dangerous than a calm one who erases a civilization, and this list is deliberately organized around consequences rather than atmosphere.
How this list was scored. Weighted on demonstrated body count and scale of destruction (40%), difficulty of being stopped (30%), reach and infrastructure (20%) and how close they came to total success (10%).
Media mix: Film (5), Comics (4), Anime (4), Video games (3), TV (2), Literature (1), Animation (1).
Iron Man #55 · 1973
He succeeded. Half of everything died, and the story had to spend an entire additional film undoing it.
Superman's Pal Jimmy Olsen #134 · 1970
His objective is the permanent removal of free will from every thinking being in existence, and he pursues it on a geological timescale.
Game of Thrones · 2012
Fighting him increases his army. Every strategy that works against a normal enemy actively helps him.

He converted a galactic democracy into an empire and built a weapon that destroys planets. The scale of harm is difficult to overstate.

He is the rare villain who actually destroys the world in the middle of his own story. The second half of the game is played in the ruins.

He is not malicious, which is why he ranks here instead of first, but his arrival is an extinction event for whatever planet he reaches.

Planetary genocide as a commercial operation, carried out repeatedly across an empire that spans a galaxy.

He nearly took an entire world twice, and the only counter required carrying his weapon into his own territory on foot.

One specimen loose in a closed environment ends everyone in it. The danger is that the species scales through any host population it reaches.

Every demon in the world is an extension of him, which means the threat has been growing continuously for a thousand years.

He sacrificed an army of people who loved him and then returned as a head of state with genuine popular support. The damage is both physical and moral.

Nothing in his world can physically stop him, and he controls the media that would report what he does.

A continent of undead under a single will, capable of raising every casualty of every battle he loses.

A hundred-year war of extermination already in progress, escalating to a plan to burn an entire continent.

He hunts down and kills an entire religious order and enforces the destruction of populated worlds. His personal reach is the empire's reach.

A single unit that cannot be stopped by any weapon available to the people it is hunting, and it can look like anyone they trust.

He set a meteor on a collision course with his own planet as a step in a plan to become a god.

The body count is enormous and almost none of it is traceable to him, which makes him arguably the hardest villain here to stop.

He has attempted human extinction on multiple occasions and cannot be permanently destroyed, only postponed.

The smallest scale on this list and still one of the most alarming. He does not stop, does not negotiate, and finishes contracts nobody is paying for anymore.
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