This Congressional Research Service (CRS) report describes the history and duties of the Director of National Intelligence, as well as of the Office of the Director of National Intelligence. It also describes how Congress has played an influential role. From the Document: "The United States Intelligence Community (IC) is a collection of 18 statutory elements within 6 cabinet departments and an independent agency that all carry out intelligence-related functions. As provided in statute, the Director of National Intelligence (DNI) oversees the integration of these intelligence functions, spearheads the support the IC provides to the military and senior policymakers across the government, and serves as principal intelligence advisor to the President."
CRS In Focus, IF10470
Congressional Research Service: https://crsreports.congress.gov/