a tricky deceitful fellow
"A knave, a rascal, an eater of broken meats; a base, proud, shallow, beggarly, three-suited, hundred-pound, filthy worsted-stocking knave ..." William Shakespeare, King Lear, 1605-6
"A pro-Romney political action committee, Restore Our Future, spent more than $4 million ensuring that Iowans couldn't watch 10 minutes of television without being assaulted by an ad explaining why Gingrich was a scoundrel, a knave, a hack, a goon or shudder a closet liberal." Eugene Robinson, The Washington Post, January 4, 2012
About the Word:
The Bard was particularly fond of the word knave it crops up throughout his plays. One of the oldest words in English, knave comes the Old English cnafa, meaning "boy" or "male servant."