I assume you're referring to the popular Korean historical drama "Dae Jo-yung" or "Dae Jo Yeong". The drama is a historical epic that tells the story of the Goguryeo kingdom and its legendary founder, Taejo of Goguryeo, also known as Dae Jo Yeong.
The drama originally aired in 2016 on KBS2 and consisted of 50 episodes. If you're looking for English subtitles, I can guide you on where to find them: Dae Jo Yeong English Subtitles