Wigger I (died 981) was the father of a line of counts ruling from his new castle of Bilstein, west of Albungen (today part of Eschwege) to the Werra. The counts of Bilstein played a prominent role in Thuringia from 967 to 1301 and were third after the Ekkehardinger and Weimar-Orlamünde in terms of power and influence.
Wigger was probably the second son of Siegfried, Count of Merseburg, and thus a nephew of Gero the Great. On his uncle's death in 965, he was granted the March of Zeitz. For a time he was also the Margrave of Merseburg and possible also of the March of Meissen. He had extensive estates — Langensalza, Mühlhausen, Schlotheim, Frieda, Dornburg an der Saale, and Eschwege — and comital authority in the Eichsfeld and the middle Werra. He was count of the Germarmark (east of Mühlhausen), Weitagau, and Ducharingau (area of Zeitz and Naumburg). He was also the advocate (vogt) of the Diocese of Zeitz.
He was a faithful follower of the Ottonians. He participated in their wars on the Slavic peoples to the east and was created count in the Plisnagau and the Puonzowagau. He and his brother Dedi founded the convent of Drübeck near Wernigerode. In 981, Wigger gave his propriety interests in the convent to Otto II.
Wigger died in 981 and was succeeded in the Germarmark and the Watergau by his son Wigger II. His march was bestowed on Ricdag and the remainder of his possessions went to Eckard I of Meissen.