Why does Ender call himself “Speaker for the Dead”?

Ender writes a book based upon the knowledge he gathers from the queen, telling the entire bugger history, especially their sorrow that the two races could not understand each other, and signs it SPEAKER FOR THE DEAD. The readers of the book form something of a religion on earth, but on the colonies, where people live in worlds that the buggers lived in, the teachings of the book become a veritable religion. Ender speaks to Peter once (who is now in his seventies because the relativistic ride that took two years for the colonists was fifty earth years), and his brother tells him his story. Ender writes this up in a book as well, signs it with the same title, and the two books are the basis of the religion. Finally Ender convinces Valentine to fly with him to different worlds. He is looking for a place to start a new bugger civilization, and his search lasts many years.

Ender writes a book based upon the knowledge he gathers from the queen, telling the entire bugger history, and signs it SPEAKER FOR THE DEAD.