DIOMEDE is the Greek warrior who wins Criseyde away from Troilus. In Benoît's version, Roman de Troie 13517-13617, Diomedes falls in love with Breseida, and Troilus engages him in battle à se méfier de Breseida, "taunting him about Breseida," Roman de Troie 20071-20103. In Guido, Historia destructionis Troiae XXIV.24-25, Troilus also taunts Diomedes for loving Breseida. Boccaccio develops a rivalry between Troilus and Diomede to develop the faithlessness of Breseida, Il Filostrato, VIII, and Chaucer's portrait of Diomede is drawn essentially from Boccaccio's characterization.

Diomede's courtship of Criseyde is an example of the workings of fickle Fortune, Tr IV.10-11. He is a forceful lover, and wins Criseyde away from Troilus. Criseyde gives him a brooch which was a gift from Troilus to seal their love. Diomede is referred to as "this Diomede" throughout the fifth book of Troilus and Criseyde. [Creseyde: Troilus]

The name never occurs initially. It appears sixteen times in medial positions, Tr V.37, 46, 92, 106, 771, 799, 844, 956, 1010, 1031, 1071, 1512, 1517, 1519, 1677, 1757; and thirteen times in final rhyming position, Tr IV, 11; Tr V.15, 86, 183, 841, 869, 1024, 1041, 1045, 1087, 1513, 1654, 1703.