Juno is a member of the First Civilization and a member of the Capitoline Triad, alongside Jupiter and Minerva, that created the Pieces of Eden in the Assassin's Creed franchise.
During the Human-First Civilization War, the members of the Capitoline Triad hid underground, safely avoiding the fighting, as they researched methods of salvation from the First Disaster. Failing to find a solution, the catastrophe killed nearly all First Civilization and mankind.
Thousands of years later, Juno contacted Clay Kaczmarek and Desmond Miles to warn of the impending catastrophe's return and help the Assassin's retrieve the Apple of Eden. With the Apple in hand, the Assassin's raced to the Grand Temple to stop the catastrophe.
Finding the key, by accessing the memories of Connor Kenway, Desmond and the others entered the inner chamber where Juno and Minerva appeared. Minerva revealed that Juno was imprisioned in the Grand Temple for using the Pieces of Eden to try and conquer the world and enslave humanity. Desmond, choosing to release Juno and save humanity, sacrificed himself to save the world in the hopes that Juno could be stopped.
