Admiral, a naval officer of the highest rank. The word comes from the Arabic amir-al-bahr (commander of the sea). In the U.S. Navy there are five grades of admiral. The highest ranking is admiral of the fleet, which corresponds to general of the army. An admiral of the fleet wears five stars. The other ranks are: admiral (four stars); vice admiral (three stars); rear admiral (two stars); and rear admiral lower half (one star). All admirals are called flag officers, and when aboard ship display a flag with the appropriate number of stars.

In the 19th century and in World War II U.S. Navy officers in the one-star pay grade bore the rank of commodore. In the postwar years, until 1982, the grade existed only for pay purposes; the rank of rear admiral had two pay grades, the lower being that of a commodore. The commodore rank was reactivated in 1982 but in 1986 its name was changed to rear admiral lower half.

David G. Farragut was the first United States naval officer to become a rear admiral (1862), vice admiral (1864), and admiral (1866). In 1899 Congress gave George Dewey the special rank admiral of the navy, the highest rank ever held by a United States naval officer. The five-star rank was created in 1944. William Leahy, Chester Nimitz, and Ernest J. King were the first to hold it.