Complex sentence: A regulatory agency (also regulatory authority or regulator) is a government agency that regulates an area of human activity by codifying and enforcing rules and regulations, supervision or oversight, for the benefit of the public at large.
Split into simpler sentences: A regulatory agency (also regulatory authority or regulator) is a government agency responsible for administrative law--that is, regulation or rulemaking. Regulatory agencies deal with areas of human activity by codifying and enforcing rules and regulations and imposing supervision or oversight for the benefit of the public at large.