According to the current US President, Barack Obama, he looks upon Mahatma Gandhi and Nelson Mandela for the transformation in him.

Gandhi And Mandela Are Obama's Heroes
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Along with Abraham Lincoln, US President Barack Obama also looks up to Mahatma Gandhi and Nelson Mandela as his heroes for bringing the transformative change without violence by changing people's minds and hearts.
"Abraham Lincoln is probably the President who I find most compelling because not only did he deal with probably the biggest crisis in American history, the Civil War, but he also did so in a way that was full of understanding of humanity," told Obama.
"And his willingness to, I think, understand other people, from slaves to slave owners, and try to hold people together even when we were in the midst of war I think is extraordinary." "Internationally - Nelson Mandela, Mahatma Gandhi. I always am interested in leaders who are able to bring about transformative change without resort to violence, but rather changing people's minds and people's hearts," Obama said. 
The White House released the transcript of his interview on Sunday, a few hours before Obama heads to Russia for his first trip as president.