Andrew Wakefield.
A quick rundown:
1. Made millions of dollars on a scheme that essentially involved torturing small children for money. He invested heavily in a company producing MMR vaccine alternatives, then falsified research to claim the current MMR vaccine causes autism in order to drive people to purchase his product. Said falsified research involved performing spinal taps on small children, a very painful procedure.
2. His claims about a vaccine - autism link provided credibility to the anti-vaccination movement where none existed before, spurring hundreds of thousands of parents to refuse to vaccinate their kids and causing a resurgence of nearly-eradicated illnesses. Tens of thousands of child deaths can be directly linked to him and his fraud. He's probably killed more people than first world terrorism has in the past century, but he's still a millionaire and the only consequence he's suffered is losing his medical license.
