Short answers, pulled from the story.
The earliest surviving Robin Hood ballad is "Robin Hood and the Monk", preserved in Cambridge University manuscript Ff.5.48, written after 1450. It contains many elements still associated with the legend, including the Nottingham setting and the enmity between Robin and the Sheriff.
In the earliest ballads, Robin Hood is clearly a yeoman, meaning neither a knight nor a peasant. The elevation of Robin to the nobility, specifically as the Earl of Huntingdon, began in the 16th century with Richard Grafton's Chronicle at Large and was popularised by Anthony Munday's 1598 plays.
The first printed version of a Robin Hood narrative is A Gest of Robyn Hode, dated to around 1500. The first clear written reference to "rhymes of Robin Hood" appears in the alliterative poem Piers Plowman, thought to have been composed in the 1370s.
Historians generally regard Yorkshire, specifically the medieval forest of Barnsdale, as the probable origin of the legend. The earliest Robin Hood type place-names are concentrated in West Yorkshire, and A Gest of Robyn Hode is written in a northern dialect identified as probably Yorkshire. The first Robin Hood place-name in Sherwood Forest does not appear until 1700.
Joseph Ritson was a scholar who in 1795 published an influential collection of 33 Robin Hood ballads titled Robin Hood: A collection of all the Ancient Poems Songs and Ballads now extant, relative to that celebrated Outlaw. His edition provided English poets and novelists with a convenient source book and directly influenced Walter Scott's depiction of Robin Hood in Ivanhoe in 1818. Ritson's own political views as a supporter of French Revolutionary principles shaped his interpretation of Robin Hood as a heroic opponent of tyranny.
The Green Feather Movement was a campus protest against McCarthyism and book censorship in the United States. It began at Indiana University Bloomington after a Republican member of the Indiana Textbook Commission called in 1953 for a ban on Robin Hood from all Indiana school books, citing alleged communist connotations. Within weeks the protest had grown into a nationwide campus movement.