Khafre (2558 - 2532BC), built the Great Sphinx as part of his funerary complex, for the large part of its history it has been covered in sand (the Dream Stela of the Sphinx records how the young Tuthmosis IV removed the sand from around the body of the sphinx and so became Pharaoh).
The Sphinx itself is about 66ft (20m) high and 240ft (73m) in length. It has suffered much through the years - the desert winds have caused erosion, various people throughout the ages have added to the damage also (the face was damaged by religious fanatics in the 14th Century AD), the French army of Napeolon used it for target practice in 1798.

Putting a face back on the Sphinx:
By taking the face of Khafre's statue found in his Valley Temple, scaling, adjusting colours etc it is possible to see what the face of the Sphinx originally looked like ... perhaps...
It is noticeable, however, that the remaining features of the sphinx do vary slightly from the statue of Khafre (the face is more rounded and fuller, the eyes are wider apart and bigger - matching the features of Khufu more closely) - but this can quite easily be put down to the difficulties of working on a scultpure many times bigger than the original.