Leo Diogenes (Greek: Λέων Διογένης, Leōn Diogenes), styled as Porphyrogenitus, was the son of Byzantine Emperor Romanos IV Diogenes and Eudokia Makrembolitissa. Probably crowned co-emperor during his father's reign, he later served in the armies of Emperor Alexios I Komnenos. He does not appear on any of Romanos' coins, although there is at least one letter that refers to him as emperor (basileus). Anna Komnene notes that he and his brother Nikephoros both wore the diadem and tzangion (red sandals) usually reserved to emperors.
|Co-emperors||Romanos IV (1068–1071)|
Michael VII (1071–1078)
Leo's father, Romanos IV Diogenes, died while Leo was still an infant. Although elevated to the rank of co-emperor on his birth, he was banished to a monastery along with his mother after the fall of Romanos. Here he remained until the accession of Alexios I Komnenos in 1081, who took in Leo and his brother Nikephoros and raised them like his own sons.
According to Anna Komnene’s account, Leo was a committed supporter of Alexios, who urged him not only to confront the Norman invaders early in his reign, but also the Pechenegs who had invaded the empire from beyond the Danube in 1087. During one of the pitched battles against the Pechenegs, Leo allowed himself to be drawn away from the emperor's side, and as he approached the wagons of the enemy, he was struck down and died on the field of battle.