The characters of mathematics to be discussed are not persons, though mathematics has more than its share of that type of character, but the building blocks of its notation. These questions may easily be thought trivial, until you consider them for a while. They generated some of the heftiest controversy there was in the course of developing the MathML specification.
Notation is very important for mathematics.
It has helped both to advance and to impede it over the years. Good notations are part of the effective abstraction mechanism underlying the progress of mathematics and science in general. What notation MathML enables, and perhaps even the unforeseen uses of it, may determine how fast MathML catches on. MathML already offers notations of new types as well. This should be part of the basis for MathML's success and widespread adoption.