Diem, Ngo Dinh, 1901-63, president of South Vietnam (1955-63). A member of an influential Roman Catholic family, he was a civil servant before World War II and was connected with the nationalists during the war. He repeatedly refused high office with the government of Bao Dai until 1954, when he became prime minister. In 1955 he controlled a referendum that abolished the monarchy and emerged as South Vietnam's ruler. With strong backing from the United States, Diem initially made some progress, but his favoritism toward his family and toward Roman Catholics over Buddhists caused substantial criticism by the early 1960s. Opposition grew as Diem's authoritarianism increased and as South Vietnam's position in the Vietnam War deteriorated. With the apparent connivance of the U.S. government, a group of dissident generals staged a coup in 1963, and Diem was murdered during the takeover.

(born Jan. 3, 1901, Quang Binh province, Viet.—died Nov. 2, 1963, Cho Lon, S.Viet.) President of South Vietnam (1955–63). Of noble birth, Diem was on friendly terms with the Vietnamese imperial family and served as Emperor Bao Dai's minister of the interior (1933), but he resigned when the French would not accept his legislative reforms. He turned down an invitation to join Ho Chi Minh's forces and lived in self-imposed exile until invited back in 1954 by Bao Dai to serve as prime minister of South Vietnam. In 1955 he ousted the emperor and made himself president. He refused to carry out elections mandated by the Geneva Accords of 1954, ruled autocratically, and showed preference to fellow Roman Catholics in an overwhelmingly Buddhist country. An unpopular leader, Diem was assassinated by his generals in 1963.

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Diem may refer to several different people or phrases:

• Ngo Dinh Diem was the leader of the Republic of Vietnam who was assassinated in a military coup in 1963.
• Ryan Diem, player in the NFL
• Carl Diem, originator of the Olympic torch relay

Diem (nominative case: dies) translates to "day" in Latin and is used in several phrases:

• Carpe diem, a Latin phrase meaning "seize the day"
• Per diem, meaning "per day"
• De die in diem, meaning "from day to day"