Loan shark

A loan shark person is a person who lends money at exorbitant interest rates and is an American expression first attested from the early 20th century. Long before this, the figurative use of shark to describe a predatory person or predatory behaviour, was and still is Standard English, and dates from 1600s. The specific meaning of shark to describe unscrupulous moneylenders and usurers also dates from the early 18th century.