Thomas de Leu or Leeuw or Le Leup (1560–1612) was a French engraver of Flemish origin.
He began his career in Antwerp, influenced first of all by Wierix. He worked mostly in Paris, starting from 1576, at the atelier of Jean Rabel. He was one of the most important engravers of portraits of his time. He was the son-in-law of Antoine Charon, one of the principal painters of the Second School of Fontainebleau, and, thereby, brother-in-law of the engravers en taille douce Léonard Gauthier and Jaspar Isaac. He was also the father-in-law of Claude Vignon.
As one of the most important engravers of his time, de Leu's pieces are highly sought after. Some of his more famous subjects include Claude de Sainctes, Jacques of Savoy, several plants for Mattias de Lobel's Plantarum Seu Stirpium Icones, and, interestingly enough, himself.
Of the engravings from the period, the plate for his self-portrait is by far the most sought-after, as only a few prints of the portrait exist, likely given as gifts to family members and close friends originally, and the existence of the plate has apparently never been acknowledged. Many sixteenth century engraving enthusiasts have speculated as to where the plate is, and in such circles questions of its location/ownership can go on for hours, generating wild conspiracy stories and even hypotheses about now-unknown printing methods used by De Leu.