Guy Tachard (1651–1712), also known as Père Tachard, was a French Jesuit missionary and mathematician of the 17th century, who was sent on two occasions to the Kingdom of Siam by Louis XIV. He was born in Marthon, near Angoulême.In 1680, Tachard went to the Caribbean (Antilles) with Jean II d'Estrées.Tachard was involved in embassies to Siam, which came as responses to embassies sent by the Siamese King Narai to France in order to obtain an alliance against the Dutch.