The King, the Queen, the Chairman of the Board, the Pit Boss, the CEO, the Pope, the Greg Brady, the Grand Poobah of swear words.
Fuck is also onomatopoetic.
Take the scene outside the bowling alley in Chasing Amy. Fucks, well chosen and used sparingly, can spruce up a dull fucking paragraph like a sonofabitch. Shit is good. Shit is explosive and emotionally clear. But shit is a little bit lazy, I think.