Brahmagupta

An Indian astronomer who wrote the first rule-book for two strange new ideas: zero as a number, and negative numbers as the answers to subtractions that go below it. Before Brahmagupta, a question like what is 2 minus 5? simply had no answer. He worked out the rules (like two steps backward then three more lands you five steps backward) and the whole left side of the number line was opened up.