Panaenus was an Athenian painter active in the 5th century BC, working alongside Polygnotus and Micon. He matters because he took part in major public decorations in Athens and Olympia during the era of the Persian Wars.
According to ancient sources, he was the brother of Phidias, although Strabo describes him as his nephew and collaborator. In the Stoa Poikile, the painted colonnade in the Athenian Agora, he depicted the Battle of Marathon in a wide range of colours, and he is said to have included portraits of the Athenian and Persian commanders. Micon and Polygnotus may have assisted him there. At Olympia he painted the barriers around the throne of Phidias's statue of Zeus and helped colour the figure, especially the garments. Pliny also credits him with decorating the shield of the Athena at Elis, sculpted by Colotes.
His style was probably similar to that of Polygnotus of Thasos, and both were inspired by the patriotic fervour raised by the Persian Wars. Pliny reports that he lost a painting contest to Timagoras of Chalcis at the Pythian Games. His work is known mainly through the descriptions of ancient authors.