Dietrich I was the first Count of Cleves. He reigned from 1092 through 1119. The County of Cleves (German: Grafschaft Kleve; Dutch: Graafschap Kleef) was a comital polity of the Holy Roman Empire in present Germany (part of North Rhine-Westphalia) and the Netherlands (parts of Limburg, North Brabant and Gelderland). Its rulers, called counts, had a special and privileged standing in the Empire. The County of Cleves was first mentioned in the 11th century. In 1417, the county became a duchy (German: Herzogtum Kleve; Dutch: Hertogdom Kleef), and its rulers were raised to the status of Dukes.

Its history is closely related to that of its neighbours: the Duchies of Jülich, Berg and Guelders and the County of Mark. In 1368, Cleves and Mark were united. In 1521 Jülich, Berg, Cleves and Mark formed the United Duchies of Jülich-Cleves-Berg. The territory was situated on both sides of the river Rhine, around its capital Cleves and roughly covering today's districts of Cleves, Wesel and the city of Duisburg. He was succeeded by his son Arnold I, Count of Cleves.