Passage: Kazi Nazrul Islam (Bengali: কাজী নজরুল ইসলাম, pronounced [kazi nozrul islam]; 25 May 1899 – 29 August 1976) was a Bengali poet, writer, musician, anti-colonial revolutionary and the national poet of Bangladesh. Popularly known as Nazrul, he produced a large body of poetry and music with themes that included religious devotion and rebellion against oppression. Nazrul's activism for political and social justice earned him the title of "Rebel Poet" (Bengali: বিদ্রোহী কবি; Bidrohi Kobi). His compositions form the avant-garde genre of Nazrul Sangeet (Music of Nazrul).Born in a Bengali Muslim Kazi family, Nazrul Islam received religious education and as a young man worked as a muezzin at a local mosque. He learned about poetry, drama, and literature while working with the rural theatrical group Letor Dal. He joined the British Indian Army in 1917. After serving in the British Indian Army in the Middle East (Mesopotamian campaign) during World War I, Nazrul established himself as a journalist in Calcutta. He criticised the British Raj and called for revolution through his poetic works, such as "Bidrohi" ("বিদ্রোহী", 'The Rebel') and  "Bhangar Gaan" ("ভাঙার গান", 'The Song of Destruction'), as well as in his publication Dhumketu ('The Comet'). His nationalist activism in Indian independence movement led to his frequent imprisonment by the colonial British authorities. While in prison, Nazrul wrote the "Rajbandir Jabanbandi" ("রাজবন্দীর জবানবন্দী", 'Deposition of a Political Prisoner'). His writings greatly inspired Bengalis of East Pakistan during the Bangladesh Liberation War.

Question: Besides being a poet, writer, and musician, what was Kazi Nazrul Islam most known for being?
anti-colonial revolutionary