Who is the most influential philosopher in history? Why?

Of all time? Probably Aristotle. However, you must take into account the fact that the word "Philosopher" has changed its meaning over the millennia. The Greek word meant "Lover of Knowledge" and the early Philosophers were at least as concerned with mathematics and observations of the natural world than they were with concepts such as ethics and identity. Pythagoras was accounted a philosopher, for example, but he's best known these days for his pronouncements of geometry. Ditto Euclid. Right up until the eighteenth century the word "Scientist" was unknown, and people who worked in physics, chemistry etc were known as "Natural Philosophers."

It was Plato (inspired by Socrates) who was the first philosopher in the modern sense (at least the western world), but that didn't mean he abandoned the more practical aspects of his calling. Aristotle, his pupil, straddled both worlds (though it was not a contradiction to him) and as late as the Renaissance he was known at least as much for his model of the solar system (against which Copernicus and Galileo rebelled) as his writings on morals and ethics. He was also a literary critic as well, as his works on tragedy and comedy (the latter lost) profess.

His works were well known to the Arabs of the early mediaeval period, an he was acknowledged for many centuries throughout Europe as the ultimate non-divine authority.

Having said that, very few people are influenced by Aristotle today. His works are still read, but more as historical curiosities than as useful texts.

If you want to know which philosopher has had the biggest influence within living memory, therefore - the one whose ideas (most of which have been radically twisted and subverted, by the way) have had more impact on the world today than any other - then the answer is Karl Marx.

I take it you exclude religious figures specifically to exclude the most influential philosopher in history - Confucius.

Okay, it is a tie between Aristotle and Plato then.

Good question. What is your criteria of a philosopher? What if I said Samuel Clemens? What if I said Socrates?

What if I said Martin Luther King?

The most influential? In America I believe would be ole' Abe. Way ahead of his time.

Just my opinion.

Um, why not include religious figures? Not all religious figures were philosophers, but many philosophers were also religious figures. Why should, say, Aquinas be excluded from consideration? He was a very influential philosopher.

Most Influential Philosopher

socrates, wicked midfielder too.........

Plato's work is used the most in the education field. Plato helped lay the foundations of western philosophy and science.

Socrates

Buddha the philosopher - the religion was founded against his wishes.

Either Aristotle or Plato/Socrates.