Shylock was a character from the play The Merchant of Venice by William Shakespeare.
In 2269, James T. Kirk was reminded of Shylock's demand to have his bond by Spock One's demands for Spock's destruction and his own safety. (TOS novel: Spock Must Die!)
In the mirror universe version of The Merchant of Venice, Shylock succeeded in getting his pound of flesh. (TNG novel: Dark Mirror)