Who Invented The Symbol Of Percentage?

The percent sign, %, has probably evolved from a symbol introduced in an anonymous Italian manuscript of 1425. Instead of "per 100," "P cento," which were common at that time, this author used the symbol shown.

By about 1650, part of this symbol had been changed to the form shown on the right. Finally, the "per" was dropped, leaving this symbol to stand alone, and this in turn became %. (NCTM p147)

The solidus form (%) is modern. (Smith p250)

This symbol stands for "per thousand". (Hogben p92)