Gerald of Wales´s Descriptio Kambriæ records the descent of the rulers of North Wales in reverse chronological order as follows: “David filius Oenei, Oeneus filius Griphini, Griphinus filius Canani, Cananus filius Iago, Iago filius Ythewal, Ythewal filius Meuric, Meuric filius Anaudrech, Anaudrech filius Mervini, Mervinus filius Roderici magni”.
King of Gwynedd. The Chronicle of the Princes of Wales records that "Iago son of Idwal held the government of Gwynedd after Llywelyn son of Seisyll", under 1031.
The Chronicle of the Princes of Wales records that "Iago king of Gwynedd was slain" in 1037. [The Gwentian Chronicle records that "Grufudd" defeated and killed "Iago son of Idwal prince of Gwynedd" and "took the government of Gwynedd and so became king of Wales from the Irish Channel to the Severn sea", dated to  from the context.
The name of Iago´s wife is not known. 1