He was 92.
Cosic, a former communist-turned nationalist, was one of the most influential figures in 20th-century Serbia. Cosic played an important role in the rise of Serbian nationalism in 1980s, leading to the bloody breakup of the former Yugoslavia.
Cosic joined the communist guerrilla resistance during German occupation in World War II and became a government official in charge of propaganda after the war.
At the time, Cosic had close ties with Yugoslav dictator Josip Tito.
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He served as president in 1992-1993 as most of the collapsing federation's nations already had declared independence, leaving only Serbia and Montenegro within Yugoslavia.
The transformation from a communist to a nationalist was also visible in Cosic's literary work: Gradually, he switched from novels about World War II such as "Distant is the Sun," from 1951 to works concentrating more on the Serbian way of living or war heroism, as was the case with the immensely popular trilogy "Time of Death," from the 1970s.
Cosic's support was important in the rise to power of Serbian nationalist leader Slobodan Milosevic. Liberal Serbs saw Cosic as one of the key people behind the Greater Serbia project an idea pushed forward by the Serbian nationalists who wanted to unite Serbia with Serb-populated areas of Croatia and Bosnia.
Cosic turned against Milosevic shortly before his ouster in 2000 by a popular uprising led by pro-Western reformists.