What is Gandalf's real name?

"Gandalf", "Greyhame", "Stormcrow" and "Mithrandir" are all just names that people of Middle-earth have given to the Maia spirit Olórin. Olórin, acting as one of the five Istari or Wizards, came to Middle-earth in the form of an old man to counsel the people of Middle-earth against Sauron.

For interest's sake, "Gandalf" comes from Scandinavian, "Greyhame" and "Stormcrow" are obviously English renditions, and "Mithrandir" is Elvish for "Grey-wanderer".