Deda mac Sin

Deda mac Sin (Deda, son of Sen) was a prehistoric king of the Érainn of Ireland, possibly of the 1st century BC. Variant forms or spellings include Ded, Dedu, Dedad, Degad, Dega, Dego, Deguth and Daig, with some of these occurring as genitives although usage is entirely unsystematic, besides the rare occurrence of the obvious genitive Dedaid. He is the eponymous ancestor of the Clanna Dedad,^[1][2] and may also have been a King of Munster.

Through his sons Íar mac Dedad and Dáire mac Dedad, Dedu is an ancestor of many famous figures from legendary Ireland, including his "grandsons" (giving or taking a generation) Cú Roí mac Dáire and Eterscél, "great-grandsons" (again) Conaire Mór and Lugaid mac Con Roí, and more distant descendant Conaire Cóem. A third son was Conganchnes mac Dedad. Through these Dedu is also an ancestor of several historical peoples of both Ireland and Scotland, including the Dál Riata, Dal Fiatach, Múscraige, Corcu Duibne, and Corcu Baiscind, all said to belong to the Érainn (Iverni), of whom the Clanna Dedad appear to have been a principal royal sept.

The generations preceding Dedu mac Sin in the extant pedigrees appear artificial.^[3][4] Eventually they lead through Ailill Érann to a descent from Óengus Tuirmech Temrach^[5] and thus a distant kinship with the Connachta and Uí Néill, whose own pedigree is in fact unreliable before Túathal Techtmar.

A proto-historical sept of the Clanna Dedad are known as the Dáirine,^[6] descending from Dáire mac Dedad and/or Dáire Doimthech (Sírchrechtach), and are later known as the Corcu Loígde. Alternatively this may be used synonymously, with some confusion created by their identification with the Darini of prehistoric Ulster. In any case, the Darini and Iverni are clearly related.^[7]

According to the Book of Glendalough (Rawlinson B 502) and Laud 610 pedigrees,^[8][9] a brother of Dedu was Eochaid/Echdach mac Sin, from whom descend the Dál Fiatach of Ulster. But alternatively they descend directly from Cú Roí mac Dáire,^[10] and thus from the Clanna Dedad proper. The precise relation of the Dál Fiatach to the Ulaid of the Ulster Cycle, rivals of the Clanna Dedad, is lost to history.

Eoin MacNeill finds the Conaille Muirtheimne to also descend from Dedu mac Sin, from another son Conall Anglonnach,^[11] believing they are quite mistakenly thought to be Cruthin, as found in later genealogies.

Dui Dallta Dedad was a foster-son of Dedu.

There is also an Ogham of Dedu (Ogam Dedad) found in the Book of Ogams. Over one third of all Irish ogham inscriptions are found in the lands of his descendants the Corcu Duibne.^[12]