Tomas ap Rhodri or Thomas Rothery (c. 1300 – c. 1363) was the de jure Prince of Gwynedd from c. 1325 until 1363.
Tomas was the only known son of Rhodri, the youngest son of Prince Gruffydd ap Llywelyn and younger brother to both Llywelyn the Last and Dafydd ap Gruffydd. After the deaths of Llywelyn, Dafydd, and their eldest brother Owain the Red between 1282 and 1283, Rhodri became the most senior member of the Aberffraw Dynasty to retain his liberty. He had sold his rights of succession to his brother Llywelyn around 1270 before he had had any children of his own.
Tomas was born to Rhodri's second wife in English exile 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 Wenwynwyn, 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 Is Coed (Powys). 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.
He did not make any claim himself, at least in public, to the throne of Gwynedd.
He married one Cecilia and was the father of Owain ap Tomas ap Rhodri ap Gruffudd ap Llywelyn Fawr - more commonly known as Owain Lawgoch - who in 1369 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.