The Taken King‘s Calcified fragments are sort of like the new version of the Grimoire cards in Destiny, and through these, players have discovered the backstory of The Taken King. Note: The rest of this post contains spoilers.
Essentially, some of the information found in the Calcified Fragments tells the story of how Oryx and the Hive came to be. While it’s a long story, the basic idea is this:
Way before the events in Destiny took place, the beings that eventually would become the Hive were struggling to survive on a dying planet. The fought amongst themselves, and tried to survive against predators and a toxic gas that covered the planet. In the midst of all this, Xi Ro, Sathona,and Aurash, three daughters of a dead king, decided they had had enough of all the chaos.
Aurash, the eldest daughter, ventured deep down into the planet’s core. There, she made a pact with a powerful, dark race called the Worms, who agreed to give her and her sisters great power, but at the price of them becoming hosts for the Worms. Thus, each sister was transformed: Xi Ro became Xivu Arath, Sathona became Savathûn, and Aurash became Auryx (also spelled Oryx).
The Calcified Fragments offer a much more detailed story, so if you have the time, try to collect some in Destiny: The Taken King.