William Huggins also known as Bill, was with Tom and Bert, one of the three trolls encountered by Bilbo and the Dwarves on their eastward journey to the Lonely Mountain. He seems to have been the leader of the troll-band - at least, it was he who led them to the woodlands of Trollshaws, according to his companions. It was William's pocket that Bilbo tried to pick as his first act of 'burglary', an attempt that brought the entire expedition close to disaster. Luckily, Gandalf was able to trick William and his two companions into arguing together until sunrise, whereupon they all turned to stone.
There was a real historical figure named William Huggins, a pioneering astronomer of the mid-nineteenth century, though there is no apparent reason that Tolkien based his foul-mouthed troll on this noted scientist