Hapimeses translates (loosely) as 'born of Hapi' in ancient Egyptian, much as Rameses translates as 'born of Ra' (or 'son of Ra', or a host of other options). Hapi, or Hapy (vowels are pretty much interchangable in the transliteration of ancient Egyptian), is an ancient God of the Nile (clicky); thus, Hapimeses means 'born of the Nile'. Another way of writing the 'meses' is 'moses', as demonstrated in names such as Thutmoses or Thutmose (born of Thoth, clicky). Moses, the prophet, and general chap-about-Egypt, was presumably named by Egyptians, and was drawn from the Nile by them, which the 'moses' part could clearly signify. So, Hapimeses, as in 'born/drawn from the river Nile' is possibly the original name of Moses, a man said to have been adopted by the Egyptian royal family.
As to why? Well, in a roleplaying game I ran over a decade ago the man behind the Moses myths featured prominently. I used the name a great deal back then on gaming forums, and have been using the name ever since.
