I don't see this as the easiest question in the world to answer. On face value, it is not that difficult. Emerson is probably the thinker with whom the movement is strongly associated. He was one of the first, if not the first, to write extensively on the topics of the Transcendentalist movement and is easily the most quoted writer from the Transcendentalist period. Emerson represents the standard Transcendentalist and most people associate him with the lasting legacy of the literary movement. Yet, if we are examining the Transcendentalist movement's legacy and its most profound impact on American society, and which thinker did the most to advocate this element of the movement in a memorable manner, I think that Thoreau becomes the most famous Transcendentalist thinker. Thoreau's ideas on civil disobedience, protesting in the name of what is right, and ensuring that one's name is associated with the best of one's actions, Thoreau has a more famous legacy than Emerson. Thoreau keys into the uniquely American notion of dissent and resistance, something that caused the pivot of the Transcendentalist movement from a literary event to one of intense social change and a transformative element in politics. Emerson never envisioned this or lacked the moral courage to advocate for this. Thoreau never flinched from it. In this, Thoreau is the most famous thinker of the time period, while Emerson is probably the most famous writer of the Transcendentalist movement.