The classic United States ("US") commemorative coin series presents many individuals within its designs - colonial leaders and elected officials among them. The series did not, however, often depict a monarch/ruler on its coins, but there were three.
First was Queen Isabella of Spain; she was Queen of Castile from 1474 to 1504, and Queen of Aragon from 1479 to 1504. Isabella died on November 26, 1504.
She is depicted on the obverse of the 1893 World's
Columbian Exposition Quarter Dollar. Her connection to Columbus, and hence her depiction on a coin that commemorates the 400th anniversary of Columbus' expedition to the New World, is driven by her role in the financing of Columbus' 1492 expedition.
Contrary to the oft-repeated story of her selling/pawning her Crown jewels to finance the trip, Queen Isabella DID NOT sell her jewels/jewelry. The Spanish Crown did provide limited financial support, but Isabella's well-known support for Columbus' plan enabled primary financing to be arranged outside of the Crown via loans that were backed by expected New World riches (e.g., gold) and promised trade licenses.
1892 World's Columbian Expoaition Isabella Quarter Dollar

Next is William the Silent (aka, Prince of Orange). He was born on April 24, 1533 and died on July 10, 1584. Though not a King, William effectively functioned as a monarch while serving as stadtholder (governor) of the provinces of Holland, Zeeland and Utrecht (and later Friesland); he was appointed to stadholder by Philip II of Spain in 1559.
William led the Dutch revolt against the Spanish in 1568. The Revolt led to the Eighty Years' War (1568-1648) and resulted in the formal independence of the United Provinces (the Netherlands) in 1648. The result of the Revolt is the source for William's popular moniker of "Father of the Netherlands."
William is depicted (rear portrait) on the 1924 Huguenot-Walloon Tercentenary Half Dollar along with Admiral Gaspard de Coligny.
1924 Huguenot-Walloon Tercentenary Half Dollar

The third ruler depicted on a US commemorative coin is Cecil Calvert. Cecil served as the First Lord Proprietor of the Province of Maryland for 42 years - 1632 to 1675. Though he wasn't a king, he was given sovereign authority over the Colony (aka, palatinate powers) over the colony by King Charles I. He had the authority to coin money, establish courts, wage war and collect taxes.
1934 Maryland Tercentenary Half Dollar

For other of my posts about commemorative coins and medals, including more about each of the coins referenced here, see:
Commems Collection