Unico Wilhelm, Count van Wassenaer Obdam (30 October 1692 – 9 November 1766) was a Dutch nobleman who was a diplomat as well as a composer. He reorganized the Bailiwick of Utrecht of the Teutonic Order. His most important surviving compositions are the Concerti Armonici, which until 1980 had been misattributed to the Italian composer Giovanni Battista Pergolesi (1710–1736) and to Carlo Ricciotti (1681–1756).
Van Wassenaer was born into a distinguished family of wealth, power and accomplishment—the House of Wassenaer. His grandfather, Jacob van Wassenaer Obdam, was supreme commander of the confederate Dutch navy, and was killed in battle in 1665 in the Second Anglo-Dutch War; his father, Jacob van Wassenaer Obdam (younger), served as a general of the army in the War of the Spanish Succession, but ruined his military reputation in 1703 in the Battle of Ekeren, and spent the rest of his career as a diplomat.
Unico Wilhelm van Wassenaer was born in the family castle of Twickel, near Delden, on 30 October 1692, the son of Jacob van Wassenaer Obdam (1645–1714) and Adriana Sophia Raesfelt (died 1694). He grew up in the Hague, where he was taught to play the harpsichord and violin. In 1707-09 he stayed with his father and three sisters in Düsseldorf at the court of Johann Wilhelm, Elector Palatine. The strong Italian influences at the court had a major influence on his musical development.
On 18 September 1710 Unico Wilhelm was admitted to the University of Leiden to study law.
In December 1711 he interrupted his studies to go to Frankfurt for the coronation of the Emperor Charles VI.
In June 1713, after completing his studies, he returned to Düsseldorf where his father and sisters had settled.
He may have accompanied Arent van Wassenaer Duyvenvoorde on a visit to Britain in 1715–16.
He made a grand tour of France and Italy in 1717–18.
In 1723 Unico Wilhelm married Dodonea Lucia van Goslinga (the daughter of Sicco van Goslinga), with whom he had three children.
Unico Wilhelm had inherited the estate of Twickel from his father in 1714 and three years later was admitted as a knight of Overijssel.
He lived in this region from 1719 to 1724, when he accepted a position in Holland.
His older brother Johan Hendrik found him a position as water manager of the Rhineland (1723), counsel to the Admiralty (1724) and governor of the Dutch East India Company (1734). These jobs kept him in and around the Hague. After his brother died in 1745 he moved into the Van Wassenaer house in the Kneuterdijk.
A year later he was admitted into the Dutch knighthood. Unico Wilhelm continued to spend part of his time at Twickel, and in 1726 he had maps made of this property and the rest of his inheritance.
In 1744 Unico Wilhelm was sent on a diplomatic mission to the French court, and in the autumn of 1744 and again in 1745 he was sent to the court of Clemens August, Elector of Cologne. In 1746 he went again to France, and finally in 1746–47 to Breda for further discussions with the French.
Although clearly intelligent, Unico Wilhelm was not a natural diplomat.
Unico Wilhelm was a commander of the Bailiwick of Utrecht of the Teutonic Order.
He was made coadjutor in 1753, and introduced administrative and managerial innovations. In 1761 he was made Commander of the order.
He died in The Hague on November 9, 1766.