Theodoric I (c. 916 – c. 976), German Dietrich I, also known as Thierry I of Liesgau, is considered the oldest traceable member of the House of Wettin.
Almost nothing is known about Theodoric's life; not even the year of his death is clear. It is believed that he was killed in battle with the Hungarians in 976. He had two sons:
- Dedo I, Count of Wettin (died 1009)
- Frederick I, Count of Eilenburg (died 1017), who had no sons
Because of Theodoric's importance to the genealogy of European royalty, much speculation exists about his ancestry. Three possible fathers have been identified for him, but there is no conclusive evidence for any of them:
- Dedi I, Count in the Hassegau (died 960), a descendant of Burchard, Duke of Thuringia
- Burchard III, Duke of Swabia (died 926)
- Volkmar I, Count in the Harzgau