How did Elvis change the World, with his music and his life?

I don't think that prior to Elvis, any entertainer had such world wide aclaim, he did bring people together. While other entertainers, did the whole cross over thing from music to movies, etc, he was as you mentioned the phrase "elvis has left the building"

He touched people's lives in a personal way, such as the gifts he gave he was known for buying others a car,

prior to Elvis, no one had built a following around the world as he did, and the crowds he generated etc, I think lead the way for others to make it so big.

There are people who were inspired by his music, and who knows how many lives he changed in little ways due to this.

Elvis legitimized Rock and Roll and made it mainstream where it used to be just back alley music played by blacks and renegade whites like Bill Haley and the Comets. He made it truly universal and for the first time there was mass appeal instead of just underground movements.