This thesis will explore a particular aspect of the life and ideas of Leon Trotsky, one of the most important historical figures involved in the history of class struggle. As a Marxist revolutionary for forty-two years, Trotsky's political work embodies all of the crucial strategic experiences and lessons of the working class in the twentieth century. Specifically, this thesis will explore the penetration of undercover state police agents into the Trotskyist movement, both before and after Trotsky's assassination in Coyoacan, Mexico. From an historical standpoint, this thesis depicts how Trotsky's assassination was the culmination of a Stalinist war against Marxism. Moreover, it shows that the continued penetration of the Trotskyist movement after Trotsky's assassination by Stalin's secret police (Hereinafter, GPU), as well as by the American Federal Bureau of Investigation (Hereinafter, FBI) represented a war against the most threatening expression of working class politics. These are not simply important historical questions given that all of the fundamental class antagonisms existing then still remain. As social unrest engendered by the staggering degree of social inequality continues to erupt, governments around the world respond with systematic political repression.