Board Thread:Boruto Discussions/@comment-34938099-20180619182027/@comment-5311048-20180620163719

The first ever person to awaken the Rinnegan could be Momoshiki, or one of his ancestors before they were absorbed. But the first person on earth is Hagoromo. After him it's Madara. So we are not entirely sure who had the Rinnegan first. But it might be safe to assume that it was one of the early Otsutsuki clan members before Momoshiki.