Karros was an Immortal born in Andrianopolos, Thrace in the year 115 BC. At some point in his life he was sold into slavery by the Romans. He was purchased and taken to a gladiator school (possibly in Capua) where he was trained to become a gladiator. Around the year 73 BC, Karros died fighting in one of the gladiatorial games and became Immortal. He was soon taught about his heritage by another gladiator, Obelix the Gaul. After a while, Karros met fellow Thracian, Spartacus, and joined him when he started a slave rebellion against Rome.