The Blades of Chaos is the weapon of choice by Kratos in the first God of War game.
Kratos was once a captain in the Spartan army with only 50 soldiers, but soon the number rose to the thousands. His tactics were brutal and effective, he was feared by everyone, except one, his wife. His army had been undefeated until they faced the Barbarians, where Kratos would lay before the Baraian King, presumably defeated, however, in the last moment, before the fatal blow, Kratos pledged his life to the God of War, Ares, in return of enough power to defeat his enemies. In that moment, Kratos became a servants of Ares, as his reward, Kratos got the Blades of Chaos seared into his arms and thereby becoming an extension of himself.
God of War
In God of War, the Blades of Chaos is the primary weapon of Kratos, they can be used in various combos, discover secrets, and they are often to execute devastating and, somewhat, humoristic animations sequences in boss battles as well. The Blades can be upgraded do inflict more damage and unlock different combos.