Who was king of the gods according to the Vedas?

The king of the Gods of India was, and is still, Indra the Rainmaker. Curiously, he's not the highest God, since the Trimurti of Brahma, Vishnu and Shiva is still higher. This curious state of affairs is the result of the Aryan invasions, which brought new deities into an established hierarchy. Rather than try to displace the native gods, their simply affixed theirs to the top of the hierarchy, much the same as the kings and queens of Britain would later set themselves over the native princes, shahs and rajahs.