Eberhard I of Nellenburg was a nobleman from the House of Nellenburg, a family that played a significant role in the history of Swabia in present-day Germany. He is known for his leadership during the late 12th century and for his efforts to expand the influence of his family in the region. Eberhard I's reign was marked by alliances and conflicts with neighboring nobles, which were common during this period. His legacy includes the establishment of the Nellenburg castle, which served as a stronghold for his family and a symbol of their power in the area.