Otto I, Landgrave of Hesse

Otto I (c. 1272–1328) was landgrave of Upper Hesse from 1308 and reunited the landgraviate by inheriting Lower Hesse in 1311 after his half-brother John's death. A son of Henry I the Child, he held Marburg and Giessen and ruled from Kassel.

He waged a long feud with Archbishop Matthias of Mainz, losing Giessen briefly in 1327 before its citizens restored it to him, and won a victory at Wetzlar, after which King John of Luxembourg mediated a settlement in 1328. He died at Kassel and was buried in Ahnaberg monastery.