Mark Johnson, 38, charged up to 8000% in interest on loans of between £100 and £500. He targetted the poor, the sick and people on social security benefits. Victims' benefit books were used as security and he made "chilling and disturbing" threats to force them to repay debts.
Birmingham City Council's specialist loan shark investigation team estimated that father of two Mr Johnson had profitted to the sum of around £800,000 and had spent up to £40,000 each on a BMW 300 convertible and Porsche Cayenne sports car.
On sentencing Mr Johnson, Birmingham crown court Recorder Andrew Tidbury told him: "You preyed on the weakest members of the community. These were people who had no one else to lend them money.
"It was suggested you were doing them a service. The reality was to the contrary. You were lending money at exorbitant rates of interest with terms of repayment they would find impossible to comply with."
Johnson admitted carrying on a consumer credit business without a licence, blackmail, possessing criminal property, attempted deception and unlawfully obtaining a disability benefit book.