Who found the Constellation Pegasus?

Answer 1

Nobody "found" it; it was there all along. Constellations don't really exist; there are no animals and heroes in the sky. We _think_ we see those things in the night sky because we humans are exceptionally good at seeing patterns - even when there is no pattern.

A couple of thousand years ago, before there was TV, or movies or the internet, people entertained themselves and others by making up stories. Some of the stories were of the everyday sort, and some were fantastic stories about heroes, gods, and astounding animals. Without artificial light, people who were out away from their campfires could see millions of stars, and sometimes they would make out the patterns of those animals, like a flying horse in the sky, and either make up stories about them or incorporate them into their stories.

That's where our constellations come from.