Decades before the Conflux, Crucius devised the magical alloy etherium and began a grand project to infuse living things on Esper with it. Crucius proposed this Noble Work as a means to overcome the frailties and limitations of the mortal flesh, but he may also have perceived Esper's disconnection from two crucial elements, red and green mana. Indeed, the aether inside etherium may have been intended to enable a spell that would reunify Esper with the other shards.
The Ethersworn blamed Crucius for etherium abominations called aether-liches, terrible creatures who resulted from an over-application of etherium and Crucius disappeared, considered to be an enemy of the plane. Esperites believe him to be in hiding, or dead. In truth, he may have left Alara altogether.