The Wikipedia says the following:
The name Ozymandias (or Osymandias) is generally believed to refer to Ramesses the Great (i.e., Ramesses II) , Pharaoh of the Nineteenth dynasty of Egypt. Ozymandias represents a transliteration into Greek of a part of Ramesses's throne name, User-maat-re Setep-en-re.
See
http://en.wikipedia.org/wiki/Ozymandias
Rene
www.AboutNames.ch