John I of Mecklenburg

John I of Mecklenburg, called the Theologian (c. 1211 – 1 August 1264), was the eldest son of Henry Borwin II and ruled as Lord of Mecklenburg from 1234. He fought at Bornhöved in 1227, where the Danish defeat freed his land from Danish suzerainty.

He had ruled jointly with his brothers before the division of 1234, when he kept the ancestral lands. In 1255, after his brother Pribislaw I lost his lordship, John received Sternberg in the ensuing division.

He promoted the Church and German settlement in Mecklenburg, where Slavs still predominated, and in 1262 allied with the Guelphs against Denmark. He was buried in Doberan Minster.