If you mean "original" to be at the forming of
Arda, he was a
Maia named
Mairon, and could "dress" himself in any form he wanted. He abused his power and as
Annatar, gained the trust of the
Elves of Eregion, and later of the
Kings of the Numinorians. When Numinor was destroyed,
Sauron lost his body, and his ability to assume a fair form. When
the One Ring was cut off his hand he again lost his visible form, and as most of his power was in
the Ring, it took a long time for him to regain his strength. Eventually he took the form of the Necromancer, and when he was driven from Dol Goldur he went to
Mordor. I'm not sure his physical shape is ever described, except as a Dark Shaddow. The famous Eye was his
symbol. When the One Ring was destroyed, he lost his ability to take on physical form, and became, as
Gandalf put it, "
a mere spirit of malice that gnaws itself in the shadows, but cannot again grow or take shape"