Who is the main character in the book, The Humans: A Novel?

The narrator's name is never known. We only that he has been beamed to earth in order to complete a mission in the guise of Professor Andrew Martin. Despite inhabiting his body, and to all the other characters actually being him, the personality manifesting through Martin is that of the alien.

The character development of the narrator is one of the more interesting in the novel because the "line" between him and the real Andrew becomes increasingly blurred, and by the end of the novel this character actually "becomes" Andrew, in a sense.