King received his BA degree at the age of 19 and then trained as a minister for three years, going on to take a PhD at Boston University. In his desire to challenge the condition of America, he studied ethical thinkers from Marx to Plato, but the one who had the greatest impact on him was Gandhi.

Gandhi's non-violent protest had gained India's independence from Britain, inspired by Jesus's sermon on the mount – which King felt Gandhi understood better than Christians.

"Prior to reading Gandhi, I had concluded that the ethics of Jesus were only effective in individual relationships. The 'turn the other cheek' philosophy and the 'love your enemies' philosophy were only valid when individuals were in conflict with other individuals; when racial groups and nations were in conflict, a more realistic approach seemed necessary. But after reading Gandhi, I saw how utterly mistaken I was."

Determined to put this "love ethic" of Jesus into practice to change America, he rejected offers of academic posts and returned south. He married Coretta Scott in 1953, and in 1954 became the minister of Dexter Avenue Baptist Church in Montgomery, Alabama, where he worked with such campaign groups as the National Association for the Advancement of Colored People.

Then on 1 December 1955, Rosa Parks, a local black woman, got on a bus. By law, blacks were bound to vacate the middle section of the bus when the whites-only part was full, but for once she refused and was arrested.

King and other black leaders met in his church and decided it was time to act. They called a boycott of the buses, electing King as their leader.

It was a phenomenal success. For almost a year, hardly a single black person in Montgomery rode a bus. Cheap taxi services were organised, which the city authorities closed down. Car pools started up instead. The bus company was devastated, but the city fought all the way.

Throughout, King insisted that they reject violence in favour of Christian love.

"It was the Sermon on the Mount," he said, "that originally inspired the negroes of Montgomery to dignified social action. It was Jesus of Nazareth that stirred the negroes to protest with the creative weapon of love... I came to see early that the Christian doctrine of love operating through the Gandhian method of nonviolence was one of the most potent weapons available to the negro in his struggle for freedom."

Next: Winning the Montgomery bus boycott