A more thorough explanation:

A quadruplator is a person who could bring criminal charges against someone and receive a reward of one-fourth of the value of the thing they accused the person of. This was usually related to fraud against the government.

For example, in ancient Rome, if someone reported that a person was committing fraud against the government, they could become a quadruplator and receive a reward of one-fourth of the value of the fraud. This created an incentive for people to report crimes against the government.