Gamwell was the name of a noble family in the Nottinghamshire area, possibly the Earls of Mansfield. The older RH stories say that RH was the son of a daughter of that family and was raised in Warwickshire (at Locksley, perhaps). He spent one Christmas in Nottinghamshire with his mother's family, where he defeated numbers of blokes his own age in demonstartaions of skill, sport etc, until he came across a page-boy called Little John, a giantic youth. Eventually, and after a hard time, RH beat LJ as well. RH's uncle Gamwell asked him what reward he would like and RH claimed LJ as a gift.
Later, when RH & LJ were outlawing about the forest, they ran across the famous pedlar. The pedlar was, in fact, a bloke called Gamwell, a cousin of RH, who had been exiled from England 'for killing a man on my father's land' (exiled instead of hanged because he was of Gamwell blood, no doubt). Returning to Britain illegally, he heard that cousin RH had set up as an outlaw and went to look for him. Once he and RH had established their relationship he was permitted to join the gang.
RH, in the older tales, did not wear Lincoln Green, but scarlet. The rest of the gang wore green. Because of his family relationship with RH, Gamwell the 'pedlar' was also permitted to wear scarlet, and became known as 'Will Scarlet'.