Elros brother of Elrond being crowned king of Numenor by who? the Valar? by the Edain? It's weird how he went from being raised by Maglor and Maedhros to becoming the first king of the most powerful nation of Men.
From Akallabêth, the fourth part of The Silmarillion:
At the feet of the mountain were built the tombs of the Kings, and hard by upon a hill was Armenelos, fairest of cities, and there stood the tower and the citadel that was raised by Elros son of Eärendil, whom the Valar appointed to be the first King of the Dúnedain.
So the answer is the Valar. Whether it was any Vala in particular, Tolkien didn't say, but it seems likely that the appointment of Elros was decided by all of them together as a body.