Echol Cole and Robert Walker were two sanitation workers killed in Memphis, Tennessee on Tuesday, February 1, 1968. The deaths of these men, together with many numerous racial and working-class injustices, prompted Martin Luther King, Jr. to join a citywide march on March 18 to honor these men, support the Memphis Sanitation Strike, and address the human rights violations that led to their deaths. The march ended with police action, but another was scheduled. King was assassinated the evening before the second march.
From Taylor Branch’s On Canaan’s Edge (ISBN ), page 684: