1. Megacles was possibly a legendary Archon of Athens from 922 BC to 892 BC.
2. Megacles was a member of the Alcmaeonidae family, and the archon eponymous in 632 BC when Cylon made his unsuccessful attempt to take over Athens. Megacles was convicted of killing Cylon (who had taken refuge on the Acropolis as a suppliant of Athena) and was exiled from the city, along with all the other members of his genos, the Alcmaeonidae. The Alcmaeonidae inherited a miasma ("stain") that lasted for generations among Megacles' descendants.
3. Megacles, the grandson of the above and member of the Alcmaeonidae family, was an opponent of Pisistratus in the 6th century BC. He drove out Pisistratus during the latter's first reign as tyrant in 560 BC, but the two then made an alliance with each other, and Pisistratus married Megacles' daughter. Herodotus claims that they also tricked the Athenians into believing Athena herself had arrived to proclaim Pisistratus tyrant, by dressing up a woman named Phye as the goddess. This event is subject to debate as to whether Herodotus has interpreted this episode correctly. However, Megacles turned against Pisistratus when Pisistratus refused to have children with Megacles' daughter, which brought an end to the second tyranny.
This Megacles later competed circa 560 BC or later with Hippocleides, a former archon of Athens, to marry Agarista, the daughter of Cleisthenes of Sicyon. They had two sons; the elder Hippocrates was father of another Megacles (ostracized 486 BC) and a daughter Agariste was mother of Pericles and Ariphron (himself the father of Hippocrates of Athens who died 424 BC). The younger son Cleisthenes was allegedly father of Deinomache (or Dinomache), mother of Alcibiades (d. 404 BC). Thus, Megacles the elder was great-grandfather of Pericles and Alcibiades.
4. Megacles, grandson of the above, son of Hippocrates, and brother of Cleisthenes was ostracized in 486 BC. He is sometimes described as the father of Deinomache and thus the maternal grandfather of Alcibiades. Other sources, notably William Smith, insist that his uncle Cleisthenes was the grandfather of Alcibiades.