Characters of Supernatural - Leviathans

Leviathans

Leviathans were first introduced as another primary "creation" of God—already including humans, angels, and demons—during the season premiere of Season 7. According to Death, the Leviathans were among God's earliest creations but were sealed in Purgatory because they were a threat to His other creations. Castiel accidentally absorbs them, along with the souls in Purgatory, during his attempted apotheosis, and the Leviathans free themselves. Once free, they organize a hierarchy with the Leviathan possessing the businessman Richard "Dick" Roman as the leader, though Crowley claims that this being has always been their leader.

The Leviathans are portrayed as virtually indestructible, voracious, and stronger than demons and low-level angels. They can shape-shift into humans, but to do so, they must use traces of their DNA. Leviathans not only replicate the corporeal form of a human, but also their memories and skills. They also have the ability to punch into an angel, killing it. Leviathans' weaknesses include magic and borax and decapitation, though none of these are lethal. One way for a Leviathan to die is for it to be eaten by a Leviathan. They can commit suicide by eating themselves. Late in season seven, the characters find a tablet containing the "Word of God" that reveals a Leviathan can be killed by using "a bone of a righteous mortal washed in the blood of the three fallen." When this happens in the season finale, the Leviathan liquefies and explodes. Killing Roman, the only Leviathan leader that there has ever been, severely weakens the Leviathans as they are now directionless. According to Crowley, they will now be regular monsters, albeit ones that are much harder to kill.

In season seven, the Leviathans, led by Roman, plan to turn humankind into a farmed, Leviathan food source. They intend to do so through chemically decreasing their intelligence via food adulterants and curing their diseases, including cancer. The Winchesters put a stop to this during the season finale, with Dean and Castiel killing Roman, which, as a side consequence, sends them to Purgatory. The remaining Leviathans are apparently slaughtered by Crowley and his demon army. By season 8 the next year, all the Leviathans influence appears to have disappeared from the Earth.

Not all Leviathans may have escaped from Purgatory through Castiel as four were seen there during Dean and Castiel's time in the realm, attacking them. Castiel indicates that there are even more and states that they are relentlessly hunting him. One of his last memories before escaping Purgatory is of Leviathans chasing him. This could also be explained by the fact that, being monsters, when they die they return to purgatory.