| Otto III of Ravensberg | |
| Noble Family: | House Calvelage-Ravensberg |
| Father: | Louis, Count of Ravensberg |
| Mother: | Adelheid of Dassel |
| Spouse: | Hedwig of Lippe |
| Burial Place: | Church of St. Mary in Bielefeld |
Otto III of Ravensberg ( - 5 March 1306) was Count of Ravensberg from 1249 until his death.
Otto III was the son of Count Louis of Ravensberg and his wife Adelheid of Dassel. His younger brother Louis was bishop of Osnabrück.
After his father died in 1249, there were some problems with his succession. Since he and his brothers were still minors, Lord Bernard III of Lippe took up the regency for Otto III and his brothers Louis and John. Their mother, Adelaide, fled with her children to her relatives in Ratzeburg, whereupon Bernard forcibly occupied Ravensberg Castle. Eventually, Otto III was installed as Count of Ravensberg.
In 1264, Otto III was victorious in a feud against the Count of Gesmold. In 1267, he fought on the side of Archbishop Engelbert II of Cologne in the Battle of Zülpich.
After Count Henry IV of Oldenburg-Wildeshausen died in 1270, Vlotho Castle came into the joint possession of Otto III and his cousin Henry of Berg. In 1290, Henry's successor Gerhard sold his share to Archbishop Siegfried II of Cologne.
On 5 March 1271, Otto III married Hedwig of Lippe.
In 1277, Otto III concluded a secret alliance with Bishop Conrad III of Osnabrück, Bishop Everhard of Münster and Herford Abbey against the Lords of Lippe.
On 12 July 1293, Otto III and his wife Hedwig found an abbey at Bielefeld. It was required that the abbey house at least twelve canons. The existing Church of St. Mary was used as the abbey church. The Count of Ravensberg would hold the right of patronage.
Otto III died in 1306. He and his wife were buried in the abbey they had founded in Bielefeld. Otto's son Otto IV succeeded him as Count of Ravensberg.
On 5 March 1271, Otto III married Hedwig of Lippe ( - 5 March 1315), the daughter of Bernard III of Lippe. They had nine children: