A revolutionary person fearlessly advocates radical change. Revolutionary people and ideas challenge the status quo and might be violent or willing to upset the natural order to achieve their goals.
Like the word revolve, it's all about turning things around. Revolutionary leaders want to change the world by any means necessary. Before he was the coolest face on a T-shirt, Che Guevara was ready to die for change in South America (and in fact, he did). You don't need to be violent to be revolutionary, just ask Gandhi and Rev. Martin Luther King. You don't even need to be political. Alexander McQueen, John Lennon, and Picasso could tell you that.