[Ulvenok]

Given that none of the Valar fought in the Host of the West during the War of Wrath surely someone of sub-Valar stature must have been the one to personally best Morgoth at the end of the First Age.

I don't think he fought at all, all his minions were destroyed or fled then they cut off his legs and used his crown as a collar and threw him out of the world. He was never defeated or killed just subdued and that most likely by the other valar. I find it hard to believe that elves or maias would be able to cut off his legs and turn his iron crown into a collar. It just seems unlikely...

I'm in favor of the idea that Ungoliant and Tom Bomadil were possibly kindred spirits; both Ainu who entered Arda separately from the Valar, acting apart from them in pursuit of different motives.

It's a bit hard to put them in that ainu category, because they have both shown to be far more powerful than ordinary maias like Sauron and Melian etc. The valar are specifically those who sang the great music and neither Ungoliant or Tom were with them. One can imagine them to be similar to the valar but not really them, because they are numbered.

EDIT: I don't remember the exact phrase but I think at some point there were "other" beings or spirits that Eru sent into arda. It's very foggy, but I remember it clearly. (Not named)