In Greek mythology, Aristomachus was one of the Heracleidae, the son of Cleodaeus and a great-grandson of Heracles. He led an attempt to recover the Peloponnese during the reign of Tisamenus but, having misinterpreted the Delphic oracle, failed and fell in battle. He was the father of Temenus, Cresphontes, and Aristodemus, the three brothers who would ultimately lead the successful Return of the Heraclidae.
Adapted from Wikipedia, "Aristomachus (mythology)" · CC BY-SA 4.0
I.Family
Aristomachus belonged to the Heracleidae, the descendants of Heracles. He was the son of Cleodaeus and thus a great-grandson of Heracles, placing him in the third generation after the hero in the line that sought to reclaim the Peloponnese.
He was the father of three sons—Temenus, Cresphontes, and Aristodemus—who, in the generation after Aristomachus, carried out the successful Return of the Heraclidae and divided the conquered lands among themselves.
II.Mythology
Aristomachus led an attempt to capture Mycenae and recover the Peloponnese during the reign of Tisamenus. Before setting out he consulted the oracle, which declared that the gods granted victory "by the way of the narrows."
He understood the "narrows" to mean the Isthmus of Corinth, and on that basis the Heraclids attempted to enter the Peloponnese by that route. The interpretation proved mistaken: the expedition failed and Aristomachus fell in the battle.
His misreading of the oracle was later clarified for his sons, who carried out the Return successfully in the following generation.
III.Other figures of the name
The name Aristomachus is borne by several distinct figures in Greek mythology, and the sources keep them apart. One Aristomachus was a son of Talaus and the father of Hippomedon.
Another Aristomachus is named among the suitors of Hippodamia who competed before Pelops and was killed by Oenomaus.
These figures are unrelated to the Heraclid son of Cleodaeus and should not be conflated with him.