Lavos is the main and final enemy in Chrono Trigger. The creature crash-lands in 65,000,000 B.C. Over millennia, Lavos is burrowed deep within the planet's core, slowly draining it's energy. Lavos' energy also has an effect on the surface, being responsible for the existence of magic and the Time Gates. The monstrous creature emerges in 1999 A.D. and destroys almost everything that's left on the planet.
After Crono and his party arrive in 2300 A.D. for the first time, they discover a large computer in the Info Center of Arris Dome. It's within that computer's database that they find out an entity called Lavos destroyed the planet back in 1999 A.D. That's when Crono and his friends decided to go back in time and battle Lavos to save their future.
When the battle ends and Azala and the Black Tyrano are beaten, Azala explains that the star will crash down to earth ushering in a long ice age. Ayla mentions that in her language, "La" means fire and "Vos" means big. They soon realize that Lavos is the entity that's crash-landing on earth. Lavos descends from space in the Prehistoric era.
Later, in 12,000 B.C., Crono and his party fight their way through the underwater Ocean Palace and eventually reach the newly relocated Mammon Machine, along with Queen Zeal, Schala and the mysterious Prophet.
While the Mammon Machine is channeling Lavos' energy, Crono stabs it with the Ruby Knife. Energy is discharged and they all find themselves on a different dimensional plane where Lavos finally emerges. The monstrous Lavos easily defeats Crono's party and leaves them within an inch of their lives.
It's then that the Prophet reveals himself to be Magus in disguise. After the battle at his castle in 600 A.D., the portal transported him here to the Dark Ages. Magus then attacks Lavos but is also defeated. Lavos then tries to steal the life force from Crono's party, Magus and Schala, while Zeal stands back and laughs. Mustering some strength, Crono tries another attack, but Lavos obliterates him, leaving no remains.
The party, Schala and Magus find themselves transported back to the Ocean Palace...without Crono. Before Lavos' energy destroys the underwater fortress, Schala uses the last of her power to transport them, and Magus, to safety.
Lavos' energy is so strong that it destroys the Kingdom of Zeal floating high above the planet. The remains of the Kingdom fall to the ocean below causing a huge tidal wave to wash over most of Terra Continent.
The giant porcupine entity attacks the party, manifesting the powers and abilities of the boss enemies Crono's party faced along their journey. When the battle ends, the head of the entity disappears, leaving the empty shell.
Entering the shell, the party finds Inner Lavos, a massive two-armed creature with tubes running out of it. Destroying the arms and then the head, the battle ends and the party is transported to yet another dimensional plane where they face the Lavos Core.
The Lavos Core consists of two small floating pods with a humanoid creature in between. They realize that destroying the right pod will ultimately kill Lavos once and for all. After the battle is won, Lavos is completely destroyed and all of space and time is safe and peace is finally restored.