Fall of the Void(from Malzahar's perspective)
Long ago, in an era that history has forgotten, mortals worshiped their true gods, the Voidborn. Idols and statues were erected in their honor in the great city of Icathia, where the Voidborn's power was greatest. The Voidborn were powerful and demanded sacrifice from their worshipers. It was a small price to pay for having the honor of being in the presence of such power. But as with all great powers, there were those who thought them unworthy of being worshiped. These heretics slowly turned the Voidborn's followers against them. Of course, they didn't nearly have enough power to even touch the Voidborn. The Voidborn quickly disposed of the heretics and their armies. But they were sloppy, they didn't make sure that all of them were dead. These survivors learned of a spell that could seal the Voidborn in their home realm, The Void. It was a dishonorable trick. The Voidborn went back to The Void during the day to stay shielded from the daylight. It was during this time that the remaining heretics performed their little trick. The rift between The Void and Runeterra was sealed and the heretics thought they had succeeded. As time went on, Icathia was abandoned and left to be buried by the sands of the Shurima. History quickly turned into myth and the power of The Void was forgotten. The rift has been slowly reopening since that fateful day. The Void will return one day in full force, ready to reclaim their rightful place as gods among men. But for now, the few Voidborn who have made it back into Runeterra shall watch from the shadows, waiting for the day they can strike fear into the hearts of mortals. Until that day comes, the world powers can continue with their bickering. It will only make The Void's return that much easier. Because, as some of us now know, Oblivion awaits.
(decided to write this since we probably won't be getting new Void lore for a long time and because I love the concept of The Void)