Krios was a subject world of the Klingon Empire. In 2367, its governor, Vagh, accused the Federation of aiding the planet's rebels, who were fighting for independence from Klingon rule. However, it was eventually revealed that the Romulans were aiding the rebels with the help of Ambassador Kell. (TNG episode: "The Mind's Eye")

In 2381, Krios was conquered by the Holy Order of the Kinshaya for three months, until it was liberated by the Fifth Klingon Battle Fleet under General Klag. (ST novel: A Singular Destiny)