Llywelyn ap Seisyll

Llywelyn ap Seisyll (died 1023) was a king of Gwynedd in the 11th century who ruled over the Welsh kingdoms of Gwynedd, Powys and Deheubarth.

Biography
Llywelyn was the son of Seisyll, about whom little is known. He first appears on the record in 1018, when he defeated and killed Aeddan ap Blegywryd and his four sons, subsequently obtaining control of Gwynedd and Powys.

In 1022, Rhain the Irishman, who claimed to be a son of Maredudd ab Owain and thereby asserted a claim to Deheubarth, was made its king. Rhain's claim was contested by Llywelyn, as Maredudd's daughter Angharad was Llywelyn's wife. A battle ensued at Abergwili in 1022, where after significant casualties on both sides, Rhain was killed and Llywelyn took control of Deheubarth.

According to the Brut y Tywysogion, Llywelyn's reign was prosperous, and he was dubbed "King of the Britons" by the Annals of Ulster. Llywelyn passed away in 1023, and despite his accomplishments, his son Gruffydd did not immediately succeed him, potentially due to his young age.

Legacy
Gruffydd would eventually become the first and only ruler to govern the entirety of what is now known as Wales, although he was killed by his own men in 1063. His sons, Maredudd and Idwal, met their end in 1069, fighting at the Battle of Mechain.