Mindaugas (also known as Mindowe (Polish), Mendog (Polish, modern), Міндо́ўг (Mindoŭh) (Belarusian), Mindovg (Russian)) (c.1203 - 1263) ruled Lithuania as grand duke ("didysis kunigaikštis", "вялікі князь") from c.1236 and as king ("karalius", "кароль") from 1253 until he renounced his Cristianity in 1262 and again became grand duke of Lithuania.

He united local tribal "duchies", conquered Black Ruthenia.

He and his wife Morta were baptized around 1252 by the bishop of Kulm (now Chelmno) in the presence of the Master of the Livonian Brothers of the Sword. A member of the Order named Christian was consecrated as first bishop of Lithuania.

This raised a huge opposition and the Baltic peoples continued to resist conversion to Christianity, and after defeat by pagan forces in 1260, Mindaugas renounced Christianity. He was killed by his nephew Treniota and Duke Daumantas of Nalšiai. Under the usurper Treniota, of strong paganist beliefs, the country relapsed into paganism until the conversion (1386) of grand duke Jogaila.

Only with Gediminas, grand duke from 1316, did Lithuania's revival begin. While most of Lithuanian grand dukes from Jogaila onward reigned also as kings of Poland, their titles remained separate, and Mindaugas was the only true King of Lithuania.