The mysterious Infinity Stones finally have an origin story of their own - along with the all-powerful Celestials of Eternals fame, and the two are inextricably connected. The six stones (called gems in the comics until very recently) are ferociously-powerful items that allow a wielder to control a fundamental aspect of the Marvel Universe (Space, Time, Reality, Mind, Soul and Power). Defenders Beyond #2 reveals important facts about both the stones and the Celestials - as well as their dark purpose in both the MCU and the comics.
In the Marvel Cinematic Universe, the Infinity Stones have existed on film since 2011's Captain America: The First Avenger (the Space Stone was disguised as the Tesseract, shaped similarly to a Cosmic Cube). Little to no origin is given for the objects other than the fact that they originated during the Big Bang. Thanos sought the Stones to destroy half of all life in the universe - but unbeknownst to him, this may actually be the Infinity Stones' intended purpose. According to the Defenders Beyond series, the Stones exist specifically to destroy - which would certainly put Thanos' actions in a completely new light; the Mad Titan was only using the Stones as intended.
In Defenders Beyond #2, written by Al Ewing with art by Javier Rodriguez, the Beyonder (the villain from the 1986 Secret Wars Marvel crossover event) reveals the secrets of the Celestials and the origin of the Universe to the reader. "A strata of the earliest beings took on vibrant color, defying their monochromatic fellows," the Beyonder explains, referring to the black-and-white versions of the same beings seen in Infinity Wars. "They became the Celestials." The two beings fought in a war that defies description and created the Second Cosmos.
The monochromatic versions of the Godlike beings were seen before in Infinity Wars #5, in which Loki revealed the first Celestials were the source of the Infinity Stones - and they deposited the Stones into each universe, hoping they would eventually be used to destroy each one. While the Aspirants cannot directly wage war in person, they can create objects that others can use to cause untold destruction in their stead. Thanos is one such being, but he only seeks to eradicate half of all life - presumably, there are others in other universes who seek the outright eradication of the universe(s).
These massive revelations suggest there are two types of Celestials - one that creates and one that destroys - and the ones bent on destruction "cast stones" (as Loki puts it) into unwitting universes. Beings who seek out ultimate power such as Thanos eventually find these stones and, unintentionally or otherwise, bring about its destruction. The Infinity Stones, in the light of Defenders Beyond, are no longer artifacts of the previous universe - they are weapons of mass destruction sent by destructive Celestials.