Isabelo Rivera Negrón was the 21st Puerto Rico Adjutant General, and the commanding officer of the Puerto Rico National Guard.

The Puerto Rico Adjutant General is the commander of the Puerto Rico National Guard. As the adjutant general he is also the senior military advisor to the Governor of Puerto Rico and oversees both State and Federal Missions of the Puerto Rico National Guard. He provides leadership and management in the implementation of all programs and policies affecting more than 10,500 citizen-soldiers and airmen, and civilian employees of the three components of the PR National Guard: Puerto Rico Army National Guard, Puerto Rico Air National Guard and Puerto Rico State Guard. It is the responsibility of the Adjutant General of the Commonwealth to share his reports with the Secretary of the Army or the Secretary of the Air Force.