Proto-Korean is the hypothetical ancestor of the modern Korean language, believed to have been spoken around the 1st millennium BCE. Linguists reconstruct it by comparing similarities among Korean dialects and related languages, such as Japanese and Altaic languages. This ancient language is thought to have evolved into distinct dialects over time, leading to the formation of Old Korean and eventually the contemporary Korean language. Understanding Proto-Korean helps researchers trace the linguistic and cultural history of the Korean people and their interactions with neighboring cultures.