Who was first to say the sun is at the center?

Answer 1

Nicolaus Copernicus.

The theory that you are talking about id called the heliocentric theory, and he published his theory in 1543(if you want you can check on Google).

Answer 2

Ancient Greek philosopher Aristarchus of Samos is the first known individual to propose that the Sun is at the center of the solar system. His heliocentric model challenged the prevailing geocentric view of the universe.

Answer 3

Galileo