Bartrum's "Welsh Genealogies". His great grandfather, IDWAL ap ANARAWD, had been King of Gwynedd and Powys, however when IDWAL was killed in 942, the kingdom passed into the hands of IDWAL's cousin HYWELL THE GOOD. In 950, when HYWELL died, the kingdom passed back to Iago's grandfather, MEURIG ap IDWAL, but in 986, when MEURIG died, HYWELL's grandson MAREDUDD again regained control for that branch of the family. When MAREDUDD died without a male heir in 999, the kingdom passed back to Iago. Iago ruled Gwynedd and Powys until 1023, when a man of unknown orgins, LLWYLEYN AP SEISYLL seized control of Gwynedd and Powys. When this LLWYLEYN died in 1023 he regained his kingdoms and ruled until he was slain by LLWYLEYN's son GRUFFUDD in 1039. GRUFFUDD then became King in his place.

Iago ap Idwal was at first excluded from the throne of Gwynedd by Llywelyn ap Seisyll (also Llewellyn ap Sitsyllt) from 1018 to 1023. Iago ap Idwal was Prince of Gwynedd from 1023 to 1039 when he was murdered by Llywelyn ap Seisyll's son Gruffydd ap Llewelyn who was the only Welsh king to actually rule over the whole of Wales from 1057 until his death in 1063. Died in 1039, murdered by Gruffydd ap Llewelyn