Gruffudd Fychan I, was a Prince of Powys Fadog from 1277 to 1284. He paid homage to Edward Longshanks for the Lordship of Yale, and fought the War of 1282–1283.

Gruffudd Fychan I was the youngest of the four sons of Prince Gruffudd ap Madog, Lord of Dinas Bran. On his father's death in 1269 (or 1270) his share was the Lordship of Iâl (Yale) and Edeirnion, which included Glyn Dyfrdwy.^[1]

He was aligned to Llywelyn ap Gruffudd, Prince of Wales, against the Anglo-Normans in the Conquest of Wales by Edward I in 1277.

In the peace treaty, it was agreed that he would not do homage to Llywelyn for Edeirnion, but to Edward Longshanks to keep the commote of Iâl (Yale). He again fought alongside Llywelyn during the War of 1282–1283, and lost his lands to the English following his defeat.

Nevertheless, the new Lord of Bromfield and Yale, the Earl of Surrey persuaded the king to allow him possession of his lands, which he held from the king as a tenant at will for the rest of his life.^[2]

He died in 1289 leaving a young son, Madog Crypl, who was the heir of the Lordship of Bromfield and Yale, and the Castle of Dinas Bran, also knowned as Crow Castle.^[3]

Madog was put in the wardship of John de Warenne, 6th Earl of Surrey, who later started the construction of Holt Castle in the lordship, and commanded the Battle of Stirling Bridge against Sir William Wallace during the English invasion of Scotland.^[4] It was the First War of Scottish Independence.

His son, Lord Madog Crypl, became the great-grandfather of Lord Tudur ap Gruffudd and Owain Glyndŵr, the last native Prince of Wales.^[5]