Complex sentence: Gramsci was a most important Marxist theoretician of the 20th century, whose works are concerned with the analysis of culture and political leadership; and was notable as an original thinker within modern European political philosophy.
Split into simpler sentences: Gramsci was an important Marxist theoretician of the 20th century, whose works are concerned with the analysis of culture and political leadership. He was notable as an original thinker within modern European political philosophy.