In this detail from the "Last Supper," by Andrea del Castagno ( c. 1423-1457), we see Judas (sitting across from Jesus). The other two disciples are Peter (on the left) and John (on the right).
Castagno (also known as Andrea di Bartolo di Bargilla) created this fresco, at the Sant'Apollonia in Florence, during 1447.
Click on the image for a larger view.
Image online, courtesy Web Gallery of Art.