Robin Hood is an interesting example. There was, for a fact, a lot of "free men" that lived as robbers in that time so a figure like him can very well have existed but the tales are of course over the top. The oldest source where he is mentioned before all the romance was put in (Marion) then its just him and Little John as leaders for a band of Free men angry at the evil King. And that evil King was Edward, not John. Sadly it does not say which edward. So i think it is possible that a kind of proto-Robin Hood existed in that time but the stories are then exxagerated and later they planted them in King John And King Richard I time. The time of the Edwards was a time of high taxation because of all the wars they fought. This drove many from their homes to a life as robbers, especially during the weak Edward II that was despised by his people. The other Edwards you complained about the taxes but you respected them as Kings (at least in England, i'm sure Scotland had a very different view of it since many of the wars was against Scotland). So i'm inclined to believe (since i am of the opinion that many legends has a basis in fact) a proto Robin Hood existed in the time of Edward II and then the myth grow from there, a romantic interest was added (Marion) a big Foe (Sheriff of Nottingham) and other characters was introduced and the setting changed to a suitable chivalric era. A typical case of mythbuilding from a rather small but still factual basis.