Ottokar I, also Otakar (died 29 March 1075) was count in the Bavarian Chiemgau and Margrave of Styria from 1056 until his death.

The elder Adalbero succeeded his father but fell out with his younger brother Ottokar II during the Investiture Controversy, was banned and finally murdered in 1082.

By his mother he inherited extended allodial lands and the margravial title in the Traungau region around the fortress of Steyr.

He also served a Vogt (reeve) of the Lambach, Traunkirchen, Obermünster, and Persenbeug monasteries and was co-founder of Admont Abbey.

In the rising Investiture Controversy he remained a loyal supporter of King Henry IV.