Mahatma Gandhi is considered unique because of his insistence on nonviolent resistance to injustice, which, in his case included both his own personal trials and tribulations as a person of color in South Africa and, later, as a leader of India's independence movement.
A lawyer by training, Gandhi, who had been born in his native India, had relocated to South Africa for the Indian law firm for which he worked. Once there, he was face-to-face on a daily basis with overt discrimination against blacks, coloreds (mixed-race and South Asian), and Muslims. One of the defining moments of his life was when he was physically ejected from a train for refusing to vacate his seat in first class, a demand made of him by the racist train company. That was the start of his own personal battle with racism, which continued throughout his years in South Africa.
As white-ruled South Africa, then a British colony, continued to institutionalize racist polices, Gandhi became more active in civil rights movements. It was during his time with the British Army, serving as an ambulance driver and stretcher-bearer along with other Indian troops, that Gandhi, impressed by the firepower the British Army brought to bear against the Zulu tribes, became convinced of the improbability of overthrowing repressive, racist governments by force.
After returning to India in 1915, Gandhi devoted his life to Indian politics and the eventual decolonization of his country. Applying his theory of nonviolent civil disobedience to the situation in India, Gandhi became a leader of the anti-British movement, but one studiously dedicated to nonviolence -- an increasingly difficult stance after the Amritsar massacre of April 1919, in which British troops opened fire on demonstrating civilians, killing hundreds. [exact numbers of dead and wounded are difficult to find.]
As a political leader in India, Gandhi's role in the independence movement would grow, and included two years in a British prison for sedition. He became an increasingly prominent leader, with many followers. In 1947, India became independent, and Gandhi was a national hero, until war broke out between Indian Muslims and Hindus, with the resulting split of the country into today's Muslim-majority Pakistan, Muslim-majority Bangladesh (initially, East Pakistan until its own fight for independence from Pakistan), and Hindu-majority India, which has a very large minority Muslim population. Gandhi's advocacy of nonviolence began to infuriate Hindu nationalists, one of whom assassinated the world's greatest advocate of nonviolence on January 30, 1948.
Gandhi endured a great deal during his life, including racial discrimination, violence, and the devastating war that followed independence. Through it all, his philosophy of nonviolent civil disobedience in the face of power and repression remained firm, and survives as a symbol today.