Timeline

The Dawn

 * In the beginning there was nothing but endless Chaos, which slumbered harmoniously alongside a single immaculate pearl containing a dreaming, mighty, and unfathomable spirit known as the One, also referred to as Anu. Secretly however, a third entity stalked the infinite wastes of Chaos and began to dream of what could be.
 * At some point, this mysterious third entity quietly 'pierced' Anu's shell, causing His bottomless sea of light and potential to develop pockets of cold nothingness that eventually coalesced into dark and empty creatures driven by an insatiable hunger than whispered into Anu's ears a desire to rid Himself of any perceived imperfections, and so 'perfected' Himself by casting off all that he considered evil and wrong with Himself, resulting in what could loosely be referred to as an iteration of the 'Big Bang'.
 * Chaos awakened as a result of Anu's change, and grew offended at the sight of Anu defiling their blessed non-existence, and so began a war against Anu on the insistence of those creatures born of the 'First Evil's' meddling.
 * Anu crafted six of His shards into the Infinity Stones, while Chaos seized Anu's discarded remnants and shaped them into the first demon, Tathamet, who fought alongside the children of Chaos, immensely powerful eldritch beings known as the Outer Gods, who battled the nigh-omnipotent warriors of Anu referred to as Archangels, spawned from Anu's greatest crystalline shard.
 * Chaos's clash with Anu resulted in the creation of immeasurably powerful elemental beings of fierce astronomical might known as Primordials, who saw themselves as the children of Chaos, but the Empty Entity cared little for his new 'creations'.
 * Throughout the Great Conflict, the First Evil quietly watches from the shadows and nourishes the Void, which continues to influence the conflict on behalf of their dark master.
 * The 'Light' eventually prevails against Chaos, which they imprison within a mask-like construct that they cast into the deepest bowels of a new realm that would eventually come to be known as the Immaterium alongside its creations, the Outer Gods, behind an omnipresent veil of metaphysical psychic energy that keeps the Ancient Ones from breaking free.
 * Although they are imprisoned, vast remnants of the Chaos and the Ancient Ones' power remains in the physical realm, many of which give rise to entirely new eldritch abominations known as the Great Old Ones, while Chaos's final war cry manifests as the Darkness, the very incarnation of the primordial and all-encompassing void of nothingness.
 * To combat the Darkness, Anu, now known as the One-Above-All, gives life to the very light itself, resulting in the birth of the Angelus, who would go on to become the hated nemesis of the primordial Darkness itself.
 * During this time, Tathamet is killed in battle, and its rotting corpse and soul becomes the groundwork for what would eventually become the basis for the countless Netherworlds and Hell dimensions in Creation, while its many heads give birth to independent demonic beings known as the Great Evils, and its body swarms with festering maggots called the Shedim.
 * The scheming creatures of the Void retreat to the darkest depths of the Immaterium, where they wait in silence, steadily gathering their strength while their creator, the First Evil, silently observes Creation do its work, and takes great interest when the site of the formation of the Veil between the physical and the spiritual becomes entrenched in an exotic form of unusual energy that the One-Above-All structures, creating the Force as a method of binding Creation together and reinforcing the metaphysical barriers.
 * Sometime later, the One is surprised to discover immeasurably powerful beings of cosmic might emerge from several of His worlds. He later learns that these beings, who eventually come to be known as the Celestials, are born from the fiery world-souls of certain planets that possess unique and special traits that differentiate them from most worlds.
 * The Celestials soon take on the role on the role of universal shepherds of life and creation, and begin seeding countless worlds with life while the One retreats to a new plane of existence where He may observe his Creation unfold.
 * The First Evil continues to watch Creation and charges the Void with the corruption of a world soul in the hopes of producing a subservient Dark Celestial that they could utilize in the so-called End War, which the First hopes to achieve by manipulating the fledgling inhabitants of Creation, but sees the best way of doing so is by reincarnating himself as one of them, allowing him to experience life and creation from a whole new perspective.