The Sheriff of Nottingham is a wolf.  We never do learn his actual name.  He is a completely amoral character, devious and treacherous, while also occasionally bumbling and mildly comedic.  The most sinister aspect of the Sheriff is that he sees absolutely no wrong in exercising the duties of his office, including the collection of taxes for Prince John.  He even goes about his duties with a false modesty and cheerful demeanor, often singing or humming to himself as strolls down the streets of the village of Nottingham.  He speaks with a pronounced southwestern American accent.

It would appear that the Sheriff rose to prominence under Prince John's rulership, after King Richard left for the Crusades, as he actively works on Prince John's behalf.  He has an uncanny ability to ferret out tax evaders among the citizens of Nottingham (who all hate and fear him), but avoids armed or otherwise unpleasant conflict with them by maintaining his cheerful facade, even attempting to appear sympathetic to their plight through empty displays of concern and encouragement.  He is a very sneaky, sinister and crafty fellow.  But he also enjoys the luxuries which come from his loyalty to Prince John, and he dresses the part in his rich clothing and bric-a-brac.  To Robin Hood and Little John, he is little more than a buffoon, serving as a constant target of their pranks and heroics.  Little John even refers to him, jestingly, as "ol' bushel britches".  Conversely, the Sheriff hates those two (especially Robin Hood), and obsesses over the desire to catch or kill them. 

The Sheriff, however, can also be moved to fits of anger, and is a fairly decent swordsman and archer.  He commands the Nottingham garrison of Prince John's soldiers, and utilizes his two sidekicks, Trigger and Nutsy, both as a "brute squad" and as spies (though neither are very bright).  Most of the Sheriff's garrison consists of fellow wolves...lanky and unpleasant characters.

Origins of the character: As stated in The Robin Hood Project, by the Robbins Library of the University of Rochester (New York):

"The sheriff of Nottingham's role in the Robin Hood legends is not glamorous – nor is his rivalry with Robin Hood particularly personal. In sum, the sheriff exists because Robin Hood needs the sheriff to exist. Without a foe who embodies local and national governmental corruption, indicating both personal failings and systemic problems, Robin Hood cannot hope to stand as a resistance figure to unjust authority. Consequently, the sheriff of Nottingham is rarely granted so much as a personal name. Certainly in the late medieval / early modern ballad tradition the sheriff serves more as an incompetent stock villain over whom the protagonist – for the early Robin Hood can hardly be called a hero – continually triumphs. The narrative continuity that many modern audiences expect from serial productions on the same topic is not present in the medieval Robin Hood materials; Robin is not the same 'person' from story to story. Nor is the sheriff the same 'person': the sheriff is killed in The Geste of Robyn Hode and in Robin Hood and Guy of Gisborne because they are separate stories and are not intended to cohere."