Deioces, Diako, Diaco, Deyaco, Diyako or Deiokes (Greek Δηιόκης) was, according to Herodotus, the first king of the Medes although this is contested. In the late 8th century BC there was a Daiukku or Dayukku who was a Mannaean provincial governor. Perhaps Herodotus used the name in error.