Well, Darwin was right, but I wouldn't call him the greatest ever. It isn't like he invented the light bulb, ice cream, or general relativity.
Those are biggies, too! :P
Or penecillin and anti-biotics, the greatest achievements of the 20th century. Do we know the names of those who get credit for this? I don't, but I know the name of Darwin, the founder of the Religion of Evolution.