In the legend of Robin Hood, the Sheriff of Nottingham is the chief official whose task it is to pursue Robin Hood, who is under the ban of outlawry. His villainy often extends also to a lecherous desire for Robin Hood's girlfriend, Maid Marian. One dubious part of the legend is that many of the Robin Hood legends place him nowhere near Nottingham.
A Sherriff is the controller of a Shire (in this case Nottinghamshire). It has been and is now a real, and existing office, though one with only ceremonial duties today. The current sherriff is John Hartshorne who is also Deputy Lord Mayor of Nottingham.
There is also a book called The Sheriff of Nottingham.