Short answers, pulled from the story.
Frank Mentzer released the Dungeons & Dragons Immortals Rules in 1986. This publication marked the final chapter of the Basic Set series which had evolved from the Basic Rules of 1983 through the Expert, Companion, and Master Rules.
Frank Mentzer wrote the Dungeons & Dragons Immortals Rules and Anne Gray McCready edited the text. Harold Johnson also contributed to the editing and development process while Larry Elmore provided cover artwork and interior illustrations alongside Jeff Easley.
Characters in the Dungeons & Dragons Immortals Rules exchange experience points for power points at a rate of ten thousand to one. These characters must compete in the Olympics to advance in rank rather than following the traditional leveling system.
The history of Immortals within the Dungeons & Dragons game began with three entities who discovered the multiverse and decided to give it order and purpose. These three Immortals were the architects of the multiverse and set the stage for all future conflicts.
The Dungeons & Dragons Immortals Rules cosmology includes planes ranging from mono-spatial atto-planes which are about 1/3 inch big to penta-spatial tera-planes which are about 851 billion light-years big. An Astral Plane permeates and connects the whole of the multiverse in this system.