Henry was the second son of Landgrave
Ludwig I of Hesse and his wife
Anna of Saxony. Ludwig I had stipulated in his will that Henry and his brother Ludwig (1438–1471) should share the landgraviate equally between them, but did not concretize this provision until his death.
Ludwig II initially decided on
Lower Hesse and left Marburg and the land on the Lahn to Heinrich, where he ruled as Heinrich III. He received his nickname "the Rich" due to his marriage to Anna of
Katzenelnbogen (daughter of
Philipp I) and the territorial gains associated with it, which also came with considerable financial gain, including the lucrative revenues from
Rhine customs. The dispute over the exact division of the landgraviate between the two brothers dragged on for more than ten years. Several appraisals and arbitration awards had no effect. After initial encroachments, the conflict finally escalated in 1468/69 into an open
feud, the so-called
Hessian Brother War. A peace brokered by the third brother,
Hermann, later archbishop of
Köln, initiated renewed partition negotiations. The result was another agreement at a Diet of the Hessian
Landstände in Spieskappel Monastery, on the traditional border between Lower and Upper Hesse, in 1470. Again, some points remained unresolved. However, further discussion was unnecessary, since Ludwig II died already in 1471. Henry III took over the guardianship of Ludwig II's two sons and ruled over Lower and Upper Hesse until his death in 1483. The Marburg line became extinct with Heinrich's son, Wilhelm III, in 1500, and its possessions fell by inheritance to the Kassel line. ==Children==