Tadhg an tSleibhe was one of the few known chiefs of the Ó Fathaigh clan, located in Uí Maine, in what is now County Galway. Descendants of Fathadh mac Aonghus, they were a minor clan, based in an area called Pobal Muintir Uí Fathaigh. This is located in what is now the parishes of Kiltomas and Peterswell in the Slieve Aughty, and comprising about one thousand acres (4 km2).