Who invented base ten number system?

Answer 1

Base ten has been around for a very long time. Man has used fingers to count since the dawn of time, which is base ten.

If you mean when did the ten digits (0 1 2 3 4 5 6 7 8 9) get more or less formalized, then the credit probably goes to Indian mathematicians as zero was the last of those digits to be "recognized". By the 9th century AD rules for handling zero were well established.

In 498 AD, Indian mathematician and astronomer Aryabhata stated that "sthānāt sthānaṁ daśaguņaṁ syāt" (literally, "place to place in ten times in value"), i.e. "from place to place each is ten times the preceding" which is the origin of the modern decimal-based place value notation.