Robin Hood was a figure in folklore /pop culture, at least, dating back as far as the latter half of the 14th century (Piers Plowman, c. 1377, mentions "rhymes of Robin Hood"), and actual extant ballads about his supposed exploits dating from as early as approximately a century after Piers are still floating around. However, whether or not the songs were based on an actual person is extremely difficult to ascertain. There are mentions from legal records of the 13th century (within a century of the time generally considered "canonical" for the Robin Hood legend) of various criminals either actually named, or going by the pseudonym of, various spellings of Robin Hood or Robert Hood. It seems to have been something of a cultural meme (in the original sense, as opposed to the pepe sense.) There is also a mention of one particular "famous murderer" Robert Hood in connection to one Little John, another character from the legend, supposed to have been prominent in the later 13th century. Whether there was one primary original for the Robin Hood legend or not, and how much---if any---of the famous stories may have been based on historical fact, is something that I don't think we will ever be able to really know.