Martin Luther King Jr., Mahatma Ghandi and Henry David Thoreau all advocated for civil disobedience through non-violent means. Also, each of these individuals was, at one time or another, imprisoned for his own non-violent civil disobedience.
King is most commonly known for his leadership in the African-American Civil Rights movement. Unlike Malcolm X, who advocated a much harsher and more physically involved method of protestation, King consistently upheld that violence should never be used, even in retaliation, in efforts for social change.
History.com explains that Ghandi was the most prominent figurehead for Indian nationalism in the early 1900s, advocating for non-violent civil disobedience, passive resistance and non-cooperation toward Great Britain.
Thoreau authored an essay in 1849 called "Civil Disobedience," which calls for individuals to hold themselves responsible to justice and to their consciences before they hold themselves responsible to the government. "Civil Disobedience" also holds that if the government is not acting in accordance with justice, then the individual has a responsibility to non-violently oppose the government. King and Ghandi were both influenced by Thoreau's writings. King noted in his autobiography that Thoreau's writing was the first place he encountered the notion of non-violent resistance. In his 1907 essay, "For Passive Resisters," Ghandi praised Thoreau's practicality and morality.
Thoreau's powerful essay also influenced several other notable people, including Martin Buber, Ernest Hemingway and Marcel Proust.