Who is Zero from Zero: The Biography of a Dangerous Idea and what is their importance?

While zero is near universally regarded not as a person but as an abstract object, it is hard to see how zero could be the most important person in Zero: Biography of a Dangerous Idea. However, the author, Charles Seife, goes out of his way to treat zero as a character, to give zero a personality and to place zero within a complex plotline, so it is appropriate to treat zero as an important character.