#1 Nobody has been able to prove that he existed.
Though historians argue that the tales of Robin Hood were likely inspired by a number of Medieval, real-life outlaws, there is absolutely no historical record of Robin Hood, nor his band of merry men.
#2 Maid Marian is not mentioned in the early ballads
Maid Marian, who is traditionally considered to be the wife and partner of Robin Hood, is not mentioned in any of the early ballads or fables of the legend. Instead, she was added later due to her joint participation with Robin Hood in the May festivities of the sixteenth century.
#3 He is depicted as a noble in later legends
Later legends depicted Robin as an Earl, who turned to thievery due to the denial of his claim to an estate. This would put him above the social standard he is usually considered to have, which was that of the Yeoman, a cut above peasant but below a knight.
#4 There were many Robin Hoods
There were many Robin Hoods. Through years of research, historians made the discovery that there were actually many recorded outlaws named Robin, and with Hood being a particularly common surname in Medieval England there are quite a few to choose from. However, none of these fit the rest of the description for Robin Hood - e.g., operated in Nottinghamshire, stole from the rich to gave to the poor, his social status etc.
#5 If he existed, he probably wasn’t a hero.
If he existed, he probably wasn’t a hero. Historians have pointed out that the tales of outlaws such as Robin Hood were likely exaggerated and, if any such outlaw did exist, they were more likely to be a simple bandit or highwayman than a noble thief stealing from the rich to give to the poor.
#6 His sidekick was Little John
His sidekick was Little John. Unlike many characters who are now considered central to the myth of Robin Hood, Little John was a main star from the earliest ballads. As Hood’s trusty sidekick, Little John often got him out of trouble - including paying his ransom to free him from captivity on one occasion.
#7 It might not have been his real name
It might not have been his real name. Because the first name Robin and the surname Hood were so common in Medieval England, historians have theorised that this may have not actually been the historical Robin Hood’s (if he existed) real name, and as such this may be why the records do not list him under his famous moniker. It was fairly common practice for outlaws and other shady individuals to take on fake names in order to protect themselves during these times, so it is very plausible that this might be the case.
#8 He had no children
He did not have children. In all of the ballads of Robin Hood, he never had children. In some endings, he was killed by the Sheriff of Nottingham or betrayed by one of his allies, dying in captivity. In others, he lived a long life but simply never had children with his wife Marian. A few modern books, movies and comic books however have depicted him as having children.