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, Count of Montbéliard, and Sophie, Countess of Bar and Lady of Mousson.
| Theodoric I, Count of Montbéliard | |
| Issue: | Theodoric II, Count of Montbéliard |
| Father: | Louis of Montbéliard |
| Mother: | Sophie of Bar |
| House: | House of Montbéliard |
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 was turbulent.
In 1065 Theodoric married Ermentrude of Burgundy (1055–1105), daughter of William I, Count of Burgundy, and Stephanie. They had the following issue: