Bansky is mythic and heroic because

a
he has made millions making fun of museums and auction houses while offering the public most of his art for free.
b
his identity is unknown, yet his persona remains larger than life, and often in the news.
c
- through his own institutional critique in art, politics, and filmmaking - he subjectively improves and propels what is considered to be "art" forward.
d
all of the above.