We should probably clarify the use of the word "militant" in the question. Fundamentally, Malcolm X has to be seen as a leader that advocated resistance and actively defending oneself in the face of unrivaled brutality from both institutional means and social means of exclusion. In this light, one of the most important people that helped him embrace such a position was, simply put, racist White people in American society that he encountered. Malcolm's most basic position is one where he takes the form of defiance, what one might consider, militancy because he is exposed to a sense of discrimination and injustice around him. The Klansmen who killed his father would be one group of people that convinced Malcolm at the earliest of ages that violence against Black people was a reality in being. Another individual/ group of people who helped to move Malcolm towards a position of active dissent within the system was the insurance company who would not pay out the settlement to Malcolm's mother, arguing that Earl Little's death was a suicide, thereby they were not obliged to pay. The teachers and individuals on a personal level helped to form Malcolm's opinion that if he was not going to fight for himself no one else would was confirmed by Mr. Ostrowski, a teacher who told Malcolm that a lawyer was "not a realistic job for a nigger." Rather, Malcolm should be a "carpenter." In this, Malcolm understands that the need for active advocacy of one's self and needs must be driven internally, as the outward social order will not advocate for people of color unless it is to lock them in a socially stratified role. These individuals, at an early age, caused Malcolm to embrace the condition of active defiance that marks his adult life.