Tomas ap Rhodri (c. 1300 – 1363) or Thomas Rothery, de jure Prince of Gwynedd (c. 1325-1363) was the only known son of Rhodri ap Gruffudd (the youngest son of Prince Gruffydd ap Llywelyn Fawr, and younger brother to both Llywelyn the Last and Dafydd ap Gruffydd. After the death of both Llywelyn and Dafydd, and of their rival eldest brother Owain Goch (they all perished between 1282 and 1283), Rhodri became the most senior member of the Aberffraw Dynasty to retain his liberty because he had sold his rights of succession to his brother Llywelyn in about 1270 before he had had any children of his own.

Tomas ap Rhodri - the only son of Rhodri and his second wife - was born in exile in England sometime around 1300 and is thought to have died in 1363. He became the de jure Prince of Gwynedd after the death of his cousin Owain ap Dafydd at Bristol Castle sometime around 1325. His sister, Katherine, married into the former ruling family of Powys Fadog, now Earls of Powis. Tomas inherited his fathers lands in Cheshire and Surrey (Tatfield). However he parted from his Cheshire estates in favour of lands at Bidfield in Gloucestershire and Dinas in Mechain Iscoed (Montgomeryshire). This is not the only evidence of an enduring interest in re-establishing a base in Wales because appears to have made an unsuccessful claim on the Lordship of Llŷn on the basis that he was the heir to his uncle, Owain Goch ^[1].

He did not make any claim himself, at least in public, to the throne of Gwynedd.

He was the father of Owain ap Tomas ap Rhodri ap Gruffydd ap Llywelyn Fawr - more commonly known as Owain Lawgoch - who proclaimed himself Prince of Wales and attempted to regain the throne of Gwynedd and of the Principality of Wales itself. Owain was assassinated in 1378.