From left to right: Leviathan, Ziz, and Behemoth.
Ever since the times of pre-history, there have been tall tales of three certain monsters. One ruled the deadly waters, one the tectonic earth, and the last held their domain over the vast skies.
These were the Primordial Monsters, Leviathan, Behemoth, and Ziz, and they existed in the never-ending chaos of the Before Times, when the Universe was still in its gestation.
Leviathan was the largest of the three, and he is the source of all the tales of sea monsters that sailors have spread over the millennia. His body sprawled out for 300 miles, and his mouth unleashed plumes of flames, evaporating the sea around him and scorching ships. Other stories said he wrapped around the Earth itself and clutched onto it tightly, holding the planet together.
Behemoth was the fiercest of the three. His unrelenting anger erupting volcanoes and punching craters into the Earth's surface. He was said to be able to push the planet's own continents around and even separated them in a cataclysmic battle with Leviathan.
Ziz is the wisest of the three. Even back in the Before Times where all of them were simply rampaging beasts she held dominance over the other two. Her unrelenting winds and thunderstorms hurdled Behemoth through the air and shocked Leviathan to his very core. While Leviathan certainly dwarfs her, Ziz's size is not to be understated either. It is said a rotten egg of hers broke open when she tossed it aside, and the fluids inside it flooded an prospering ancient city.
It is told in many stories that when the world is reaching its a duel of biblical proportions with spark between Leviathan and Behemoth and the two will slay each other, bringing the planet Earth down with them. Ziz is focused on preventing this, and will force a stalemate if she has to when this happens.
While they originally started off without the ability of higher thinking, driven effectively mad with their overwhelming power, it is said that some being of even greater power brought all three of them down. Though they were spared, they were significantly weakened. This loss in power allowed for them to achieve sapience.
Currently, the three are in hiding along with the rest of the monsters in the world. Leviathan is one of the domineering monsters of the mansion that Catherine comes across. Behemoth currently lives in the massive underground base on Ni'ihau in Hawaii. Finally, Ziz does not stay in one place at once, and she usually performs regular checkups on the different bases around the world to check their condition.