Theodoric I (French: Thierry) (ca. 1045 – 2 January 1105) was a Count of Montbéliard, Count of Bar and lord of Mousson (as Theodoric II) and Count of Verdun. He was the son of Louis de Scarpone, Count of Montbéliard, and Sophie, Countess of Bar and Lady of Mousson.
After his father's death, he claimed the estate of the Duchy of Lorraine, which his father had already claimed. The claim was dismissed by Emperor Henry IV, confirming the duchy to Theodoric the Valiant. In retaliation, he ravaged the diocese of Metz, but he was defeated by Adalbéron III, bishop of Metz, and the Duke of Lorraine Theodoric the Valiant. Reconciled with the Church, he founded an abbey in 1074 in Haguenau and rebuilt the church at Montbéliard in 1080. He did not participate at the Council of Clermont in 1095, or the Crusades, but rather sent his son Louis in the Crusades. In 1100, the Bishop of Verdun gave the county to Thierry for life, but the relationship between the spiritual and temporal powers were turbulent.
He married Ermentrude of Burgundy (1055–1105), daughter of William I, Count of Burgundy, and Stephanie, in 1065 and had the following issue:
| Preceded by Louis of Montbéliard |
Count of Montbéliard 1073–1105 |
Succeeded by Theodoric II of Montbéliard |
| Preceded by Sophie of Bar |
Count of Bar 1093–1105 |
Succeeded by Reginald I of Bar |
| Preceded by Sophie of Bar |
Lord of Mousson 1093–1105 |
Succeeded by Reginald I of Bar |
| Preceded by Unknown |
Count of Verdun 1100–1105 |
Succeeded by Reginald I of Bar |