Taewang, meaning "The Greatest of all Kings", was the title used by the rulers of Goguryeo

Goguryeo

Goguryeo or Koguryŏ was an ancient Korean kingdom located in present day northern and central parts of the Korean Peninsula, southern Manchuria, and southern Russian Maritime province....

, one of the Three Kingdoms of Korea

Three Kingdoms of Korea

The Three Kingdoms of Korea refer to the ancient Korean kingdoms of Goguryeo, Baekje and Silla, which dominated the Korean peninsula and parts of Manchuria for much of the 1st millennium...

, since the reign of Gwanggaeto the Great.

Although it does not signify emperor itself, Taewang title had equal authority with Chinese Emperor.. Also some Silla

Silla

Silla was one of the Three Kingdoms of Korea, and one of the longest sustained dynasties in...

 rulers including Beopheung

Beopheung of Silla

King Beopheung was the 23rd monarch of Silla, one of the Three Kingdoms of Korea. He was preceded by King Jijeung and succeeded by King Jinheung....

 and Jinheung

Jinheung of Silla

King Jinheung was the 24th monarch of Silla, one of the Three Kingdoms of Korea.He followed King Beopheung and was followed by King Jinji . Jinheung was the nephew of King Beopheung. King Jinheung was one of the greatest kings of Silla, and was responsible for expanding Silla territory immensely...

used this title for their declaration of independence from the influence of Goguryeo.