Gero (died 11 August 979), Count of Alsleben, conjectured to be the son of Siegfried and therefore grandson of Gero the Great. If so, his mother was Hedwig, daughter of Wichmann the Elder. Gero was the brother of Tetta, who established a monastery at Alsleben in his name. 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. [Neither the identity of Waldo nor the crime are known.] At the instigation of Adalbert, Archbishop of Magleburg, and Dietrich, Margrave of the Northern March, Gero was captured at Sömmering, was placed in the custody of Thietmar's father and uncle, Siegfried I, Count of Walbeck, and Lothair I, Margrave of the Nordmark.
In accordance with the practice of trial by combat, Gero and Waldo met for a judicial duel on 11 August 979. During the fight, Gero's strikes resulted in two serious blows to the neck of Waldo, but Waldo was able to counter with a heavy blow to Gero’s head. With his opponent too dizzy to continue, Waldo left the site and disarmed, only to suddenly die of his wounds.
Despite clearly winning the combat, Gero was declared guilty and sentenced to death. On the emperor’s orders, Gero was beheaded at sunset. Apparently, the only ones pleased with the verdict were Adalbert and Dietrich. Otto I, Duke of Bavaria, who arrived later in the day, and Berthold, Count of the Radenzgau, rebuked the emperor for allowing such a man to be condemned on a petty charge. The remarkable outcome of this duel was long remembered in medieval Germany.
Gero married Adela of an unknown family. Gero and Adela had one daughter:Adela of Alsleben, married Siegfried II, Count of Stade.
No other Counts of Alsleben are recorded until the 12th century.