Why is Robin Hood popular?
Robin Hood is so popular because he appeals to so many people. Robin hood it both unfailingly good, battling for others and saving the damsel in distress. However he also is an out law and does not conform rules or society at that time. He was a thief and laughed in the face of the "law". Thus appealing to a broader audience. There is also another angle. To the English Robin Hood is an icon of the British. It wouldn't surprise me if there was a National holiday to him, before St George.
Regardless of the type of person, Goth, Criminal, Saint or average Joe, everybody is a sucker for a hero.
Ever since the beginning of the legend around the 13th century, probably based on a real outlaw, the tales of Robin Hood have been consistently popular, being 'in fashion' for 750 years.
There is no one explanation for this; rather, each generation has likely found its own 'connection' to the Robin Hood legend.
The 'first generation' of tellers of his tale may have found his appeal in his opposition to local authority and church corruption, which although seemingly incongruous today, was coupled in the earliest surviving tales with unswerving loyalty to the King and devotion to religion (especially the Virgin Mother). The very earliest possible references to Robin Hood survive as nicknames bestowed upon other outlaws during the 14th and 15th centuries, recorded for instance in court records - 'Robinhood' seems to have at one time been a byeword for 'criminal', possibly with connotations of virtue in outlawry.
However, the stories have never remained static, and just as they likely started as evolving and increasingly embellished songs and poems to be performed by minstrels, so they have continued to be developed in various different media. This process has been aided by the fact that there is no definitive tale of Robin Hood, but rather a growing collection of events and acts attributed to the outlaw, which have been continuously reinterpreted over the centuries, rather than 'stagnating' as a single unchanging entity.
One of the developments which aided the survival of the legend was its early adoption into the English May Day festivities around the 15th and 16th centuries, with Robin and his fellow outlaws quickly becoming characters portrayed by players at this time of year. This process was heightened by the apparent usefulness of the 'robbing the rich to give to the poor' motif - developed from less specific references in the ballads to Robin as a "good outlaw" - which ironically helped raise money for local churches.
Around this time also several other characters were absorbed into the legend due to their own May day appeal, including notably Maid Marian and Friar Tuck (both independent characters in their own right, Tuck likely being based on another real outlaw). The stories grew, and the deeds of others also began to be attributed to Robin, expanding the legend still further.
The stories continued to be told, and later generations continued to adapt the legend to fit with their own society and culture; for instance, the Victorian obsession with idealised British history led to our own familiar view of the outlaw as a rebel against Norman occupation of England (the earlier tales largely pitting Robin only against local authorities for local wrongs).
Today, we continue to embellish and update the stories of Robin Hood, as more and more books, TV series and movies are produced - some telling updated but traditional stories, and others inventing new ones out of whole cloth. The latest iteration of the legend is a case in point for this sort of popularity: the recent BBC adaptation, in common with all generations past, has 'updated' Robin to be a smart, hip idealist trying to keep alive and retain his principles in a hostile world run by dinosaurs and hypocrites, and the language Robin uses is that of today's younger generation.
'Twas ever thus.
Another aspect of the legend's enduring popularity, though, are its more perennial themes: preoccupations and concepts which run through the entire historical corpus of the Robin Hood legend, as relevant 750 years ago as they are today.
Justice (and injustice), social inequality, hypocrisy, abuse of power, selfishness and generosity, and defending honour and those who are unable to defend themselves, are all themes which have probably been part of the tale since its beginnings, and which we still hold dear today.
It was this coupling of an ever-changing, dynamic legend with undying themes always central to the common man which really allowed the stories of Robin Hood to reach us today; and there is no reason to think the legend will not survive another 750 years for these self-same reasons.