Who is Philip K. Dick / Horselover Fat from Valis and what is their importance?

Philip K. Dick / Horselover Fat is the novel's narrator speaks sometimes as and about himself as Phil, a successful professional science fiction author and an astute student of literature. More often he writes in the third person about his alter ego, Horselover Fat, whose name reflects Phil's own, in that Philip (Philippos) is Greek for Horselover and Dick is German for Fat. Phil claims early on to have created this character to afford himself some "much needed objectivity" (pg. 11). Early on, he fumbles back and forth between perspectives before for most of the novel sorting out that Phil is a cool, pragmatic character while Fat is disintegrating into insanity.