Naotalba is most well-known as the high-priest of Yhtill and adviser to the queen Cassilda. In the original stories of Robert W. Chambers, he (or it) is nothing more than a name mentioned without context in The Repairer of Reputations, seemingly as part of "the ramifications of the Imperial family".
'Naotalba' is the correct spelling, but the opening diphthong is sometimes reversed to read 'Noatalba', as seen in James Blish and Lin Carter's attempts to reconstruct the play, and in Fantastic Worlds. In the latter, he commits suicide by jumping from a tower window after leaving two notes, one to Uoht and one to Thale.
The Encyclopedia Cthulhiana says...Edit
That there are two individuals connected to Carcosa, probably not the same person. Either he is "High priest of Yhtill in the play" or he is "King of Carcosa who sent the 'record-keepers' out from the library of Celaeno to the far corners of the earth to disseminate the knowledge of the Great Old Ones."
If these figures are, in fact, the same person, there's a story there that has so far been left untold.