Thracians inhabited Southeast Europe including modern Bulgaria and Romania. They descended from Proto-Indo-Europeans mixed with Early European Farmers. Ancient sources described Thracians as blue-eyed and red-haired. Greeks and Romans called Thracians warlike barbarians and superior fighters. Thracians practiced polygamy, sold children, and committed human sacrifice. They tattooed bodies and valued poetry and music despite primitive reputation. Thracian mtDNA shows Western Steppe Herders and Early European Farmers ancestry. Iron Age Thracians carried mostly Y-DNA E-V13 haplogroup. Modern Bulgarians share 55% genetic legacy with Thracians and Paleo-Balkans. Thracians formed Odrysian kingdom but remained disunited and conquered by Romans. They served as elite mercenaries for Macedonians and Romans. Thracians allied with Persians against Greeks. Genetic studies link Thracians to medieval and modern Bulgarians, Romanians, Northern Italians, Northern Greeks. Thracians assimilated into Slavs, Bulgars, and Byzantines forming Southeastern Europeans. Last Thracian language use reported in 6th century AD.