Short answers, pulled from the story.
Shylock is a fictional Venetian Jewish moneylender in William Shakespeare's play The Merchant of Venice, written around 1600. He is the play's principal villain, and his defeat and forced conversion to Christianity form the climax of the story.
Shylock loans 3,000 ducats to the Christian merchant Antonio and sets the security at a pound of Antonio's flesh. When Antonio defaults, Shylock demands the pound of flesh, and the phrase has since entered the lexicon as slang for an onerous or unpleasant obligation.
Some scholars believe Shylock derives from the biblical name Salah, written שלח in Hebrew, the grandson of Shem and father of Eber. Other scholars note that Shylock was a common sixteenth-century English name of Saxon origin meaning white-haired.
Money-lending was one of the few occupations open to Jews in the Middle Ages, because Christians could not offer interest-bearing loans, then considered the sin of usury. Jews were also forbidden to own farmland, serve in government, or join craft guilds.
Edmund Kean began playing Shylock sympathetically in the first half of the 19th century, and the role established his reputation. Before Kean, the part had been performed as a repulsive clown or a monster of unrelieved evil.
The Nazis used Shylock for propaganda, and shortly after Kristallnacht in 1938 German radio broadcast The Merchant of Venice to reinforce stereotypes. Productions followed in Lübeck in 1938 and Berlin in 1940, and the Vienna Burgtheater staged an extreme version with Werner Krauss in 1943.
The name Shylock has become a synonym for loan shark, and as a verb to shylock means to lend money at exorbitant rates. It is also used to refer to any relentless and revengeful moneylender.