Was reading about him earlier today and it was stated that he was not just an accomplished tourney knight but a very good Captain/Marshal. My question is just how important was he?
The Marshal's martial prowess does tend to dominate his public image, and this is largely because we possess a biography of his life written shortly after his death which drew on interviews and discussions with members of his household.
The Marshal was entrusted with the martial training of the Young King, Henry, in 1170 and even knighted him (which annoyed Henry II, the Young King's father, no end - knighthood of a monarch was usually done by another king). The Marshal was a major landholder in Wales, Ireland, and the only magnate to hold lands in both England and France after the loss of Normandy in 1204. He played a major role in politics both local and national. David Crouch calls him, in the key period 1213-1216 the 'Pillar of the Throne' in his ODNB entry. When John I died (Oct. 1216) he was still in midst of a major conflict with his barons (which had resulted in the first Magna Carta). John had swiftly broken his vow with assistance from Innocent III. Henry III was nine years old at his ascension and William Marshal was persuaded (so his biography paints it) by the great and good of England to become his 'Guardian'. About six months into his regency of England the Marshal had brought numerous barons back into the Crown's fidelity, secured a peace with the king of France (who had been invited to rule England by the barons and actually landed soldiers in England to press his claim). The Marshal turned his attention to Wales and secured a tenuous peace with Llywelyn ap Iorwerth, ruler of Gwynedd although it was only brief by the time the Marshal died on 14 May 1219 he had secured the young Henry on his throne and successfully mended relations with the chief threats to the stability of England.