In Greek mythology, Aristomachus (Ancient Greek: Ἀριστόμαχος) is a name that may refer to:
Aristomachus (Greek: 'Ἀριστόμαχος) was a Byzantine official in Egypt. He was active in the reigns of Tiberius II Constantine (r. 574-582) and Maurice (r. 582-602). He eventually rose to become prefect of Constantinople and "curator domus Augustae" (caretaker of the household of the Augusta), but later fell out of favor and ended his life in exile. The main source about him is John of Nikiû.
Aristomachus was a citizen of Nikiû. His father "prefect" Theodosius was from Absay. Theodosius reportedly advised the young Aristomachus to rest content with the wealth and rank available to him. But the young man was exceedingly ambitious. He reportedly established his own armed following.
He seems to have held a military command in Egypt, though his rank is unspecified. He was presumably appointed by Tiberius II Constantine. John reports on his conduct: "He built vessels by means of which he could visit all the cities of Egypt with pleasure and delight. And so he became proud and forced all the military officers to be subject to the emperor; for he had received the command in the reign of the emperor Tiberius. And by reason of this command he became more and more presumptuous, and made all the troops submit to his orders, and led a fearless life. And he posted cavalry in the city of Nikiu without any authorization of the emperor. And all the troops under his command were without means, and he seized all the houses of those who were richer than he, and he esteemed them of no account. And when men of high or low degree came to him from the emperor, he let them remain at the door and did not admit them for a longtime."