Rereahu was a Maori rangatira (chieftain) of Ngāti Raukawa in the Tainui tribal confederation from the Waikato region, New Zealand. He probably lived in the first half of the seventeenth century. He is the ancestor of the Ngāti Maniapoto, Ngāti Hauā, and Ngāti Korokī Kahukura iwi, and of Rereahu, a group based around Maniaiti / Benneydale, Pureora, and Maraeroa in Waitomo District, whose status as a separate iwi or as a hapu (‘sub-tribe’) of Ngāti Maniapoto is a matter of dispute.