There are many people who could be considered the largest scammers in history, including those who ran Ponzi schemes, other financial frauds, or other types of scams
Bernie Madoff:
In 2009, Madoff was sentenced to 150 years in prison for masterminding the largest known Ponzi scheme in history, which stole over $19 billion from 40,000 investors.
M. Gregor MacGregor:
A Scottish con man who tried to attract investors to the non-existent country of Poyais
Billy McFarland:
Organizer of the Fyre Festival and other fraudulent activities that defrauded others of $27.4 million