Schala is a non-playable character in the Chrono franchise, and the prominent link between Chrono Trigger and Chrono Cross (she also appears in the Satellaview Radical Dreamers). She is the daughter of Queen Zeal in 12,000 B.C., living in the Kingdom of Zeal. She is perceived as one of the most powerful people in the kingdom. Because of this, the Enlightened Ones gave her a magical pendant that controls the Mammon Machine (a machine built to harness Lavos' energy) and certain sealed doors and chests. She is very protective of her younger brother, Janus, and as such he has a strong emotional link with her. A mistranslated line of NPC dialogue in the English localization of the game refers to them as step-siblings, but they are actually blood-related.
The Kingdom of Zeal
When she was born as Schala Zeal, it was immediately known that the gentle princess of Zeal was meant for great things. She became friends with everyone, including the Earthbound Ones (humans not possessing magical abilities, whom are looked down upon by the Enlightened Ones). The three Gurus saw this in her, and gave her the aforementioned pendant. When Crono and the party came and were captured by a mysterious prophet, Schala freed them and requested that they free Melchior (one of the Gurus, banished by a mentally deteriorating Queen Zeal). Unfortunately, the prophet discovered and sent the party back into their era.
After managing to return (by finding the Epoch), the party freed Melchior and met with Schala at Algetty (the home of the Earthbound Ones). Here, Schala talked about how she refused to activate the Mammon Machine. Dalton (Queen Zeal's right hand man) then came and kidnapped her, and forced her to turn on the Mammon Machine. This caused a large undersea palace creatively named the Ocean Palace to rise from the sea, and transported everyone around the Mammon Machine (including the prophet, now revealed to be Magus, and Crono's party). After Crono tried (and failed) to fight Lavos alone, Schala teleported everyone else away from the incident. That was the last appearance of Schala in Chrono Trigger, and until the release of Chrono Cross, it was unknown what had happened to her.
The Time Devourer
Her fate is revealed in Chrono Cross. She was transported to an area known as the Darkness Beyond Time, along with the remains of the Mammon Machine, and Lavos. Lavos took advantage of this, and absorbed Schala to create the Time Devourer (allowing Lavos to literally consume time). This caused many things to happen in Schala. She still contained some of her human feeling and emotion, but also got Lavos' hatred for the world. With her human side, she was able to assist Serge from time to time.
Before Lavos completely took over the human side of her, she managed to clone herself and send the child (known as Kid) back to 1004 A.D., where Lucca adopted her. Because of this, Serge's party was able to utilize the Time Egg and Chrono Cross to defeat the Time Devourer and in essence, fix time. They also managed to separate Schala from Lavos' evil.
In Radical Dreamers, Schala is shown to be filled with guilt for her role in the entire thing. The Frozen Flame (a part of Lavos separated, but still completely sentient) apparently reversed her age and sent her back in time to grow up as Kid.
In the DS version of Chrono Trigger, it is possible to attain a new ending with a new final boss. The player must fight the Dream Devourer, a fusion of Lavos and Schala.