Caesar Clown,who was referred to as Master by his subordinates, is a scientist, the leading expert on chemical weapons of mass destruction, and one of the co-founders of NEO MADS.

Caesar is a former colleague of Vegapunk, having worked with him both in MADS[5][13] and later the World Government research facility on Punk Hazard,[5][6] an island that Caesar went on to devastate with a toxic gas explosion,[14] earning him a bounty of Beli300,000,000.[11] Years later, Caesar returned to the island in secret to continue his illegal experiments[5] until his defeat at the hands of the Straw Hat Pirates and Trafalgar Law.

One of his projects was the production of SAD, a chemical that he supplied to the Warlord Donquixote Doflamingo to be used in the manufacturing of SMILEs, artificial Devil Fruits which were sold to the Emperor Kaidou to help create an army of Zoans. Although Caesar was briefly protected from the law by Doflamingo,this protection was lost when Doflamingo was defeated and arrested.