The home planet of the Kriosians, long at odds with neighbouring Valt Minor, and the source of the empathic metamorph Kamala and the royal heir Kaitaama.
Krios Prime is the homeworld of the Kriosians. In the Enterprise episode Precious Cargo (2152), Trip Tucker rescues Kaitaama, who is about to become First Monarch of Krios Prime, from her kidnappers.
The Next Generation episode The Perfect Mate (2368) tells how Krios and Valt Minor were once one empire, split by two brothers who fought over a woman. To end centuries of war, the Kriosian ambassador Briam brings Kamala, a rare empathic metamorph, aboard the Enterprise-D as a bride for Chancellor Alrik of Valt.
A world called Krios also appears in The Mind's Eye as a Klingon colony seeking independence. How that colony relates to the Kriosian homeworld is not spelled out on screen.