Herodotus: History

I must not omit to explain that [the tyrant] Kleisthenes picked on Melanippos as the person to introduce into Sikyon, because he was a bitter enemy of Adrastos, having killed both Mecistes, his brother, and Tydeus his son-in-law. After settling him in his new shrine, he transferred to him the religious honors of sacrifice and festival which had previously been paid to Adrastos. The people of Sikyon had always regarded Adrastos with great reverence, because the country had once belonged to Polybos, his maternal grandfather, who died without an heir and bequeathed the kingdom to him. One of the most important of the tributes paid him was the tragic chorus, or ceremonial dance and song, which the Sikyonians celebrated in his honor; normally, the tragic chorus belongs to the worship of Dionysos; but in Sikyon it was not so -- it was performed in honor of Adrastos, treating his life-story and sufferings. Kleisthenes, however, changed this: he transferred the choruses to Dionysos, and the rest of the ceremonial to Melanippos.