Theodoric I (c. 965 – between 11 April 1026 and 12 January 1027) was the count of Bar and duke of Upper Lorraine from 978 to his death.

In 985, he joined the other Lorrainer lords, including his cousin Godfrey the Prisoner, in trying to repel King Lothair of France's invasion: but at Verdun, he was captured.

Like almost all the dukes of Lorraine until the Gallicisation of the region in the thirteenth century, Theodoric was loyal to the Holy Roman Emperors.

He was captured a second time in 1018 in combat with Burgundy, but overcame Odo II of Blois, also count of Meaux, Chartres, and Troyes (later Champagne).

Theodoric married Richilde, the daughter of Folmar III, count of Bliesgau and Metz, in 985.