He is said to have been full of Christian piety despite his young age, and able to speak from the moment of his birth, professing his faith, requesting baptism, and delivering a sermon prior to his early death.

According to the 11th-century hagiography, Vita Sancti Rumwoldi, he was the grandson of Penda of Mercia (a pagan), and the son of a king of Northumbria.

[3] His parents are not actually named; the most likely candidates are Alhfrith, son of Oswiu of Northumbria, and his wife Cyneburh, daughter of Penda.

[citation needed] Rumwold is reported to have been born in Walton Grounds, near King's Sutton in Northamptonshire, which was at that time part of the Mercian royal estates, possessing a court house and other instruments of government.

[7] Church dedications largely follow the missionary activity of Saint Wilfrid,[citation needed] but once spread as far as North Yorkshire, Lincoln, Essex and Dorset.

A compilation about three saints' lives as translated by Rosalind Love shows that an unknown author "corrected" a 15th-century attribution as "martyr" (assumedly Rumbold, who was murdered in Mechelen) by annotating "confessor" .