Complex sentence: Alexander Dubček (27 November 1921--7 November 1992) was a Slovak politician and, briefly, leader of Czechoslovakia (1968--1969), famous for his attempt to reform the communist regime during the Prague Spring.
Split into simpler sentences: Alexander Dubček (27 November 1921--7 November 1992) was a Slovak politician and, briefly, leader of Czechoslovakia (1968--1969). He attempted to reform the communist regime during the Prague Spring.