Claude de Mesmes, comte d'Avaux (1595–1650) was a 17th-century French diplomat and public administrator. He was sent in various missions to Venice, Rome, Germany, Sweden, Denmark, and Poland by Richelieu. In 1635 he guided the negotiations of the Treaty of Stuhmsdorf, which extended the truce between Poland and Sweden. These two countries had fought each other in the Polish-Swedish war of 1626–1629, which had ended in a truce rather than a peace. France wanted peace between Poland and Sweden as the Swedes were fighting for France in Germany and the Poles would have menaced their flank. In 1638 he negotiated a new alliance between France and Sweden in the Treaty of Hamburg. He also was plenipotentiary at the Peace of Westphalia and ended his career as Superintendent of Finances. Birth and origins Claude was born in 1595 as one of five children, three sons and two daughters, of Jean-Jacques de Mesmes and his wife Antoinette de Grossaine. His father was knight and seigneur de Roissy, numbered Jean-Jacques II de Mesmes in the Paris branch of the family. His mother was a rich heiress, who had brought her husband the seigneuries of Avaux, Irval, Breuil, Besancourt, Bellefontaine, and Vandeuil. He appears below among his brothers as the second son: Henri (1585–1650), who was numbered Henri II de Mesmes and became président à mortier at the parlement of Paris Claude (1595–1650) Jean-Antoine (1598–1673), who inherited Henri's office of président à mortier and was the only one of the brothers that fathered sons His sisters were Jeanne and Judith: Jeanne, who married François Lambert d'Herbigny Judith, who married Judicial and administrative career He followed his elder brother Henri by starting a career at the parlement of Paris. He became maître des requêtes and then, in 1623, conseiller d'état. Comte d'Avaux In January 1638 Louis XIII raised the seigneurie of Avaux to a comté for him and his father. However, the act was only registered in 1648. Strictly speaking, Claude de Mesmes therefore became comte d'Avaux only late in his life, in 1648, whereas his father never became count as he died in 1642, well before the registration date. However, Claude de Mesmes used the title immediately in 1638 for his negotiations in Hamburg. Surely that was what the king intended. In the French version of the Treaty of Hamburg, he writes Nous, Claude de Mesmes, Comte d'Avaux, Conseiller d'Etat, whereas in the Treaty