Peter Jan Schoomaker is a retired four-star general of the United States Army who served as the 35th Chief of Staff of the United States Army from June 11, 2003, to April 10, 2007. Schoomaker's appointment as Chief of Staff was unusual in that he was recalled and came out from retirement to assume the position. Schoomaker voluntarily retired from the Army for the second time in 2007 after completing the full four-year term as Chief of Staff.

The chief of staff of the Army (CSA) is a statutory position in the United States Army held by a general officer. As the highest-ranking officer assigned to serve in the Department of the Army, the chief is the principal military advisor and a deputy to the secretary of the Army. In a separate capacity, the CSA is a member of the Joint Chiefs of Staff and, thereby, a military advisor to the National Security Council, the secretary of defense, and the president of the United States. The CSA is typically the highest-ranking officer on active duty in the U.S. Army unless the chairman or the vice chairman of the Joint Chiefs of Staff are Army officers.