Historians consider the descendants of Ednyfed Fychan, including Owen Tudor, the most powerful family in 13th to 14th-century Wales. Fychan married Gwenllian, daughter of Madog ap Maredydd. This enabled his family to act as leading servants to the princes of Gwynedd, and play a key role in the attempts to create a single Welsh principality. This privilege endured after the Conquest of Wales by Edward I with the family continuing to exercise power in the name of the king of England, within Wales. However, there remained an awareness of the family's Welsh heritage and the accompanying loyalties led them to take part in the suppressed Glyndŵr Rising.
The fact that little is known about Tudor's early life and that it has instead become largely mythologized is attributed to his family's part in the Glyndŵr Rising. At various times it has been said that he was the bastard son of an alehouse keeper, that his father was a fugitive murderer, that he fought at Agincourt, that he was keeper of Queen Catherine's household or wardrobe, that he was an esquire of Henry V, and that his relationship with Catherine began when he fell into the queen's lap while dancing or caught the queen's eye when swimming. The sixteenth-century Welsh chronicler Elis Gruffydd did note that he was her sewer (someone who places dishes on the table and tastes them ) and servant. However, it is known that after the Glyndŵr Rising several Welshmen secured positions at court, and in May 1421 an ‘Owen Meredith’ joined the retinue of Sir Walter Hungerford, 1st Baron Hungerford, the steward of the king's household from 1415 until 1421.
Henry V of England died on 31 August 1422, leaving his wife, Queen Catherine of Valois, widowed. The Queen initially lived with her infant son, King Henry VI, before moving to Wallingford Castle early in his reign. In 1427, it is believed that Catherine began an affair with Edmund Beaufort, 2nd Duke of Somerset. The evidence of this affair is questionable; however the liaison prompted a parliamentary statute regulating the remarriage of queens of England. The historian G. L. Harriss suggested that it was possible that the affair resulted in the birth of Edmund Tudor. Harriss wrote: "By its very nature the evidence for Edmund ‘Tudor's’ parentage is less than conclusive, but such facts as can be assembled permit the agreeable possibility that Edmund ‘Tudor’ and Margaret Beaufort were first cousins and that the royal house of ‘Tudor’ sprang in fact from Beauforts on both sides." Despite the statute it is accepted that Catherine married Owen at some unknown later date.
An ancient pedigree chart of the English royal family dated c.1500 states Owen Tudor and Queen Katherine had three sons, Edmund, Jasper, and Edward: “Owyn tedder marrydd wt queen Kateryn yt was wyffe un to kyng henry ye vth & had by har Edmunde yerle of rychemond Jaspar & Edward the sayd Edmund maryed wt Margarete yt was dawter & eyer un to John duke of Somersett.” . The 15th cent. Chron. of London sounds a similar note. It states that “... Oweyn hadde prevyly wedded the quene Katerine, and hadde iij or iiijor children be here.” .
Owen Tudor had at least one illegitimate child, by an unknown mistress: