Oh gosh guys I'm really sorry I'm not very good at this game, this my first time.
Was it the most potent of many? No it's not Menelmacar.
It is one of the Valar? No it's not Mandos.
Did he meet a worthy and heroic end? I'm afraid I don't know your answer. It's either really open-ended and I just haven't looked in the right places or its really specific and I haven't the time.
So the next letter is U