Queen Zeal is the ruler of the Kingdom of Zeal, a magical nation of floating continents and islands that exists in the 12,000 B.C. era of Chrono Trigger. While her husband the king was alive, she bore two children, Schala and Janus, and she was widely loved by the people of Zeal for her regal and kind personality. However, after the king died and she took the throne, her personality began a gradual shift. She decreed that Zeal would no longer require the power of the sun to provide energy to the nation, and ordered the construction of the Mammon Machine; a device capable of tapping the energy of Lavos.
She eventually becomes obsessed with power and harnessing the energy from Lavos, promising the people of Zeal that Lavos's energy would grant them all eternal life. Shortly after Crono and company arrive in 12,000 B.C., another, much larger construction project, the Ocean Palace, has just been completed, and the Mammon Machine is transported inside it at Queen Zeal's request. By this point in the game, all traces of the queen's formerly regal personality have evaporated, leaving her mad with the desire for power and willing to let her children die to attain it.
Following the Kingdom of Zeal's collapse into the ocean, she turns the Zeal Palace into the Black Omen, a floating fortress and the most difficult dungeon in the entire game. From this point on, the Black Omen appears in all time periods from 12,000 B.C. forward, with the now immortal Queen Zeal residing inside until 1999 A.D., when Lavos finally awakens. Should the player choose to end the game by completing a run through the Black Omen, Queen Zeal will appear as a boss encounter alongside the Mammon Machine.
Although she is seen as evil in the eyes of many, the three gurus of Zeal see Queen Zeal as more of a victim than an actual antagonist because of Lavos's corrupting influence on her sanity. Schala also asks for the party not to hate her mother for what she has become.