I know I'm a fan of Middle-earth, but I never got the time to become a Tolkien nerd. Let's see, read the hobbit many times, Lord of the rings many many times more (I could practically tell you anything from it) and i read the Silmarillion, once sadly. It is tedious at times, but really, when you look at it again, it's such an immense and deep, tragic tale, or tales, and better and more epic than LOTR. I've only glanced throught the HoME series, read 1 book of lost tales, and most of Unfinished tales. Then I used to regularly visit a tolkien forum, but rarely do now.
Still very interestig and neat. I wish i were a nerd.
As for Tom, Tolkien never says what he is, but from the material I think it's fair to say that either he's a mair or just a spirit of Arda created when the world was, like an enigmatic embodiment of it. Thus that makes him Eldest in Middle Earth and of it, not from the outside, as he says of the Dark Lord, Melkor.
And he's NOT a hippie bum who ruins stories! Small as his part might be, i still liked it!