Karl Marx was a 19th century German philosopher who developed influential social and political theories about capitalism and class struggle. Some key aspects of Marxist theory discussed in the document are: - Society is divided into classes based on relationships to economic systems like capitalism. - Ideology perpetuates existing power structures by making them seem natural. - Works of art and media reflect the class interests of their time and can challenge or maintain the status quo. - Material conditions directly impact people's lives and analyzing these is important for understanding society and enacting positive change.