Tulkas Purpouse

[Maédhros]

Was Tulkas forced to aid the Valar in their fight against Melkor. Was he one of the ainur that desired to be with Eru, but was forced to go to Ea and fight against Melkor.

Thus it came to pass that of the Ainur some abode still with Ilúvatar beyond the confines of the World; but others, and among them many of the greatest and most fair, took the leave of Ilúvatar and descended into it. But this condition Ilúvatar made, or it is the necessity of their love, that their power should thenceforward be contained and bounded in the World, to be within it for ever, until it is complete, so that they are its life and it is theirs. And therefore they are named the Valar, the Powers of the World.

Or did he chose in the begining to be one of the Valar.

Greatest in strength and deeds of prowess is Tulkas, who is surnamed Astaldo, the Valiant. He came last to Arda, to aid the Valar in the first battles with Melkor.