E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
It is said that poisons had no effect on Mithridates, King of Pontus. This was Mithridates VI., called the Great, who succeeded his father at the age of eleven, and fortified his constitution by drinking antidotes to poisons which might at any moment be administered to him by persons about the court. (See AQUA TOFANA.)