Meirchion Gul was probably a late 5th-century king of Rheged, a Brythonic realm in the area of Sub-Roman Britain known as the Hen Ogledd (in the North of England and Southern Scotland today).
He appears in the Middle Welsh genealogical text Bonedd Gwŷr y Gogledd as the son of the equally obscure Gwrwst Lledlwm, a grandson of Coel Hen, and grandfather of renowned Urien Rheged.
He is assumed, like Urien, to have ruled Rheged, including Catterick.
Cynfarch Oer was Urien's father.
Another son, Elidyr Lydanwyn (the Stout and Handsome), was the ruler of Rheged, according to the Gwynedd version of Hywel Dda's 'Welsh laws'.