In Chapter One of King Solomon's Mines we have the first reference to one of the main antagonists of the story:
Stop, though! there is Gagaoola, if she was a woman, and not a fiend.
Throughout the rest of the book, however, her name is Gagool. For example, in Chapter Nine:
“White people,” he said, “it passes in my mind to kill you. Gagool has spoken strange words. What say ye?”
I found but one instance where her name is not Gagool, but in that case it is not Gagaoola either; instead it is Gagoola. From Chapter Seventeen:
"Enter white men from the stars," said Gagool, advancing into the doorway; "but first hear your servant Gagoola the old.
Thus, we now have three different versions of her name, two of them being used just once apiece.
The above is all based on the Dover Thrift Edition of the book. In case this was merely the result of editorial errors in this edition, I checked two editions available online as well — Wikisource and Project Gutenberg. Notably, neither one of them had the variant Gagoola in Chapter Seventeen. However, the Gutenberg edition had Gagaoola in one additional instance, in Chapter Nineteen:
“Tell me, when thou wast little, didst thou know Gagaoola the witch doctress?”
Also, the Wikisource edition did not have Gagaoola in Chapter One. Apparently it maintained the the name Gagool throughout the book.
So what is the explanation of these variations? Is it the result of multiple editorial mistakes across multiple editions? Is it the result of an original authorial mistake (which was then either maintained or corrected in different editions)? Or is it deliberate and the character is actually meant to have variations in her name (which might either have some meaning in her native language or may be a form of endearing nicknames like Tom/Tommy)?