: Maia were Ainu who entered the "Hierarchy of Arda" in a subsidiary role to one of the Valar. The terms Vala and Maia are the equivalent of ranks in an army. As Tom was not (or ever had been) the henchman of a Vala then he could not be a Maia.

If I understand you correctly, the hierarchy of the Valar/Maiar was established at the moment of their entering Arda? Does this mean that Tom snuck in? I like 'henchman of the Valar', by the way.

:an Ainu who entered Arda, but did not join in the hierarchy of creator/guardians.
In other words, an anarchist. The question is, did he willing ignore the hierarchy or was he expelled, not necessarily for following Melkor, but for having a divergent point of view with his 'superiors'. That bring up another question: were was our yellow-booted friend when Melkor and Co. were doing terrible things in Eriador and environs?

:He enjoyed and observed the created world, indeed revelled in it, but took no responsibility for it (except in very minor ways).
A sort of John Denver of Middle-earth

Thanks for your views