I believe a mistake was made by Christopher Tolkien. I always thought Gandalf a maiar from reading the sillmarillion as Olorin was a Maiar. However, of course , our sillmarillion was not published by J.R.R Tolkien but Christopher and I believe Tolkien left us with the idea of two separate olorins in Valinor. And after reading unfinished Tales [Post LOTR writing/essays on the istari] I think J.R.R left the question open but also indicated Gandalf was valar I think his power justified that position as well. “They [Valar] sent members of their own high order [the istari], but clad in bodies as of men.” -Unfinished Tales the Istari This above passage of could perhaps be understood as a maiar as the same order as valar but it seems to go against the text. That in fact is how Christopher understood it to mean valar. Christopher noticed this “mistake” of Gandalf being a valar. Yet it came from later Tolkien writings [post lotr] and Christopher's counter and proof it was a “mistake” was his version of the published sillmarillion. Than we have this text making a better case “Who was "Gandalf"? it is said in the latter days it was believed by many of the “faithful” that Gandalf was the last appearance of Manwe himself...I do not know the truth of the matter, and if i did it would be a mistake to be more explicit than gandalf was” -Unfinished tales the Istari So Tolkien did not outright say Gandalf was Manwe [a valar] nor deny it. The argument that Gandalf was a maiar comes from his identification as Olorin. However even here does not prove him a maiar. “That Gandalf said that his name “in the west” had been Olorin was, according to this belief, the adoption of an Incognito, a mere by name. I do not [of course] know the truth of the matter.” -Unfinished tales Thus I think Tolkien left it open to what order Gandalf was but I think indicated he was a valar.