King Rhesus is a fictional Thracian king in Iliad, Book X, who fought on the side of Trojans. Diomedes and Odysseus stole his team of fine horses during a night raid on the Trojan camp.
The rhesus monkey was named after him.
And because of that, since we do not carry the D antigen once assumed present in rhesus macaques, we are in turn called “rhesus negatives”.
