"Men called [him] Bucephalus ... of the marke or brand of a buls head, which was imprinted vpon his shoulder." [Pliny, I.220, tr. Holland, 1601]"The 'buck' is any inanimate object, usually knife or pencil, which is thrown into a jack pot and temporarily taken by the winner of the pot. Whenever the deal reaches the holder of the 'buck', a new jack pot must be made." [J.W. Keller, "Draw Poker," 1887]The fig. sense of "shift responsibility" is first recorded 1912. Buck private is recorded by 1870s, of uncertain signification.
"There are in London divers lodges or societies of Bucks, formed in imitation of the Free Masons: one was held at the Rose, in Monkwell-street, about the year 1705. The president is styled the Grand Buck." ["Dictionary of the Vulgar Tongue," 1811]"The Buffs are men and boys whose love of fires, fire-fighting and firemen is a predominant characteristic." [N.Y. "Sun," Feb. 4, 1903]
Adj. meaning "well-built, hunky" is from 1980s, from sense "polish, make attractive."