Louis Althusser was a French philosopher known for his work in Marxist theory. He was born on October 16, 1918, and became influential in the 1960s with his ideas about ideology and the role of the state in society. Althusser argued that ideology shapes our understanding of the world and that it operates through various institutions, such as education and media. Althusser's most notable concepts include Ideological State Apparatuses and Interpellation, which describe how individuals are shaped by societal structures. His work has had a lasting impact on fields like cultural studies and political theory, influencing many thinkers and movements in the 20th century.