Old English wulf "wolf, wolfish person, devil," from Proto-Germanic *wulfaz (source also of Old Saxon wulf, Old Norse ulfr, Old Frisian, Dutch, Old High German, German wolf, Gothic wulfs), from PIE root *wlkwo- "wolf" (source also of Sanskrit vrkas, Avestan vehrka-; Albanian ul'k; Old Church Slavonic vluku; Russian volcica; Lithuanian vilkas "wolf;" Old Persian Varkana- "Hyrcania," district southeast of the Caspian Sea, literally "wolf-land;" probably also Greek lykos, Latin lupus).
This manne can litle skyl ... to saue himself harmlesse from the perilous accidentes of this world, keping ye wulf from the doore (as they cal it). ["The Institution of a Gentleman," 1555]
Probably extinct in England from the end of the 15th century; in Scotland from the early 18th. Wolves as a symbol of lust are ancient, such as Roman slang lupa "whore," literally "she-wolf" (preserved in Spanish loba, Italian lupa, French louve). The equation of "wolf" and "prostitute, sexually voracious female" persisted into 12c., but by Elizabethan times wolves had become primarily symbolic of male lust. The specific use of wolf for "sexually aggressive male" first recorded 1847; wolf-whistle attested by 1945, American English, at first associated with sailors. The image of a wolf in sheep's skin is attested from c. 1400. See here for a discussion of "wolf" in Indo-European history. The wolf-spider so called for prowling and leaping on its prey rather than waiting in a web.
1824, originally in African-American vernacular in the South.
The slaves themselves entertain the very highest contempt for white servants, whom they designate as 'poor white trash.' [Fanny Kemble, journal, Jan. 6, 1833]
[T]he term [poor white] is rather loosely applied by Northern writers even to mountaineers and to small farmers who live on a precarious footing. But in the Southern conception, not everyone who is both poor and white is a "poor white." To the Southerner, the "poor white" in the strictest sense is a being beyond the pale of even the most generous democratic recognition; in the negro's term, "po' white trash," or so much social débris. [Robert Penn Warren, "The Briar Patch," 1930, footnote]
"person or thing that people hope will be very successful in the near future," 1911, originally in U.S. sporting use in reference to the quest for a white man capable of beating champion pugilist Jack Johnson.