Alfred Wegener in the 50'ies
It explains that the continents of the world drift around on top of the Mantle, pretty much. It also explains why the continents fit together like puzzle pieces, because a long time ago, they were all one giant land mass called Pangea.
From Wikipedia Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912. However, it was not until the development of the theory of plate tectonics in the 1960s, that a sufficient geological explanation of that movement was found. further reading -> http://en.wikipedia.org/wiki/Continental_drift