thumb|At the Military Staff College in Iraq, 1942. Ar-Ruba'i is the third officer seated below, from the right.
Muhammad Najib ar-Ruba'i (; also spelled Al-Rubaiy; 1904–1965) was an Iraqi military officer and politician who served as the first president of Iraq, from 14 July 1958 to 8 February 1963. Together with Abdul Karim Qasim, he was one of the leaders of the 14 July Revolution that toppled King Faisal II and the Hashemite Iraqi monarchy in 1958.
While Qasim became prime minister and held most of the power, Ar-Ruba'i was elected head of state with the title of Chairman of the Sovereignty Council. The Sovereignty Council had a representative from each of the communal/ethnic groups. Ar-Ruba'i represented the Sunni community.
In 1963, Qasim was deposed in the Ramadan Revolution. This led Ar-Ruba'i to retire from politics, and he eventually died in 1965.