Robert I of Bar (8 November 1344 – 12 April 1411) was Marquis of Pont-à-Mousson and Count and then Duke of Bar. He succeeded his elder brother Edward II of Bar as count in 1352, and the county was promoted to a duchy in 1354. Their parents were Henry IV of Bar and Yolande of Flanders.
When Robert was less than a year old, his father died and his elder brother, Edward II of Bar, became Count of Bar under their mother's regency. As neither Robert nor Edward had a strong constitution, Yolande gained authorisation from Pope Clement VI to allow them to eat meat during periods of abstinence. When his brother Edward died, Robert was still only 7 years old and the problem of the regency came about again in a new form. In effect, his mother was on the point of remarrying to Philip of Navarre, count of Longueville, from the Navarre family which was struggling with John the Good for the French crown. On the other hand, Jeanne of Bar (1295-†1361), countess of Warren and daughter of Henry III of Bar, made known to the king that she was ready to take over the regency over Robert. The Parliament of Paris, by decree of 5 June 1352, decided that the county was in the king's hands. John the Good then entrusted the regency to Jeanne on 27 July that year. Yolande at first renounced the regency, but went back on her decision, levying troops to fight Jeanne. John the Good had to intervene to force Yolande to renounce the regency for good on 2 July 1353.
A question of precedence led to the County of Bar being raised to the status of duchy. In effect, Pont-à-Mousson was promoted to a margravate, the acts mentioning Robert as marquis of Pont-à-Mousson and Count of Bar. For the nobles in the County of Bar this was illogical, since to the counts Bar was territorially more important than Pont-à-Mousson. To resolve this anomaly, Emperor Charles IV of Luxembourg promoted Bar to a duchy.
Poitiers' defeat and John the Good's capture in 1356 deprived Jeanne of John's support and Yolande retook the regency, with Robert being knighted in December 1356 and declared of age on 8 November 1359. He assisted at the coronation of Charles V of France at Reims on 9 May 1364, then at that of Charles VI of France on 4 November 1380. During Charles V's reign he fought in several expeditions in 1374 aiming to eject the English from Normandy. In 1401, Robert ceded his duchy to his son Edward, but reserved the usufruct on it, bypassing his grandson Robert (son of Henry of Bar). Robert unsuccessfully opposed this in the parliament of Paris that ran from 1406 to 1409. Charles VI's madness put him under the control of the Duke of Orleans and Duke of Burgundy. Robert supported the duke of Orleans but after that duke's assassination stayed more and more in the duchy due to attacks of gout which stopped him walking.
In 1364 he married Marie Valois, daughter of king John II of France and Bonne of Luxembourg. Their children were: