Who are the Leviathans in Supernatural?

Where did the Leviathans come from?

They were God's first attempt at life. In the show's mythology they came before angels, before people and before the soul itself, and they were so ravenous that God made Purgatory to hold them, then left a way to kill them in case they ever got out. That lets the show reach past the angels and demons it had spent six seasons building and find an enemy older than all of them, loyal to neither Heaven nor Hell.

Being older than everything also explains why the usual rules fail. The weapons and wards hunters use were made with demons, angels and ordinary monsters in mind, and the Leviathans predate all of it, so the brothers' usual weapons do almost nothing to them. Their resilience is less a power than a matter of age: nothing in the arsenal was built for them, because none of it existed yet.

How did they get out?

Through Castiel. Fighting a civil war in Heaven against the archangel Raphael at the end of season 6, Castiel opens Purgatory and takes its souls into himself for the power to win, and the Leviathans come in with them; once loose, they spread through a water supply into new bodies. It is the angel's worst mistake, and the show treats it as one: the power he meant to use well carried something he could not control.

It is also a turning point for the angel himself, and the Castiel profile follows that thread. For the Leviathans, what matters is where they go next: out into the human world, wearing human faces. They can take the shape of the people they replace, heal from wounds that would end anything else, and plan on a scale the brothers had not faced before.

Why does borax hurt them?

The show hands its heroes a cleaning product as a weapon, and the joke is part of the point. Borax hurts Leviathans on contact, if only for a moment, and it is the brothers' old friend Bobby Singer who works that out. It is not a way to kill them, only to slow them, but in a season whose villains are nearly impossible to stop, a cheap powder anyone can buy gives the hunters a fighting chance and the episodes some of their darkest humour.

Borax also fits the season's theme. The Leviathans see people as food and work through the ordinary machinery of American life, companies and food additives included, so a household chemical as their weakness makes them feel embedded in that life rather than outside it. The threat and the defence both live in the kitchen cupboard, which is a very Supernatural place to put them.

What finally stops them?

A weapon God wrote down long ago. The instructions are on one of the Word of God tablets, read by the prophet Kevin Tran: the bone of a righteous mortal, washed in the blood of three kinds of fallen being. Gathering what that takes drives the end of season 7, and Dean Winchester uses it on Dick Roman in season 7, episode 23, the last episode of the season. Without their leader the Leviathans scatter, and the win costs Dean and Castiel a trip to Purgatory.

Dick Roman himself is the season's real invention. Played by James Patrick Stuart, he is a Leviathan who took the place of a billionaire businessman, and his plans run through companies, products and public influence rather than open slaughter; he is also the one who kills Bobby. Reviewers counted the performance among the season's real strengths, and the character gave the show a different kind of villain: one the brothers could not simply find and fight, because his power was spread through systems.