This depends, of course, on what movements you have studied. I will assume that you have studied both the African American Civil Rights Movement and the push for Hispanic rights. The three leaders I will pick are the obvious ones: Martin Luther King, Jr., Malcolm X, and Cesar Chavez.
I pick King because he is the face of the Civil Rights Movement. I pick Malcolm X because he represents the part of the black community that does not want to feel like it relies on or needs the white community. This sense of black nationalism was very important in the 1960s and beyond. Finally, I pick Chavez because he fought for the rights of a relatively invisible minority. Hispanics in general, and farmworkers in particular, were not very much in the public eye when Chavez mounted his effort to gain more rights and better conditions for them.