Thietmar of Merseburg, whose Chronicon is the major source of information here, refers to Gero as a Count in Northern Thuringia and Morzani.
Gero was accused before Emperor Otto II by the Saxon warrior Waldo of a crime.
At the instigation of Adalbert, Archbishop of Magdeburg, and Dietrich, Margrave of the Northern March, Gero was captured at Sömmering and placed in the custody of Thietmar's father and uncle, Siegfried I, Count of Walbeck, and Lothair I, Margrave of the Nordmark.
[2] In accordance with the practice of trial by combat, Gero and Waldo met for a judicial duel on 11 August 979.
With his opponent too dizzy to continue, Waldo left the site and disarmed, only to suddenly die of his wounds.