Caspar Willard "Cap" Weinberger (August 18, 1917 – March 28, 2006) is an American politician and businessman.

As a prominent Republican, he serves in a variety of state and federal positions for three decades, including Chairman of the California Republican Party, 1962–68.

Most notably he is Secretary of Defense under President Ronald Reagan from 1981 to 1987.

Weinberger was born in San Francisco, California.

He serves in the 41st Infantry Division in the Pacific theater of the Second World War.

Weinberger's entry into politics is as a California State Assemblyman from 1953 to 1959, and he goes on to serve as Chairman of the Federal Trade Commission and Director of the Office of Management and Budget under Presidents Richard Nixon and Gerald Ford.

An accomplished private sector businessman, he later becomes vice president and general counsel of Bechtel Corporation, and still later Chairman of Forbes magazine.

Weinberger's tenure as Secretary of Defense is marked by his hard line against Soviet Russia, in disagreement with the State Department.

He promotes the Strategic Defense Initiative.

He is indicted in the Iran–Contra affair but never convicted.

Weinberger is awarded both the Presidential Medal of Freedom in 1987 and an honorary British knighthood from Queen Elizabeth II.