No one was the leader, NBK was a product of both minds and it happened for the anger of both, and as thedragonrampant wrote, Eric was the owner of the practical and Dylan of the metaphysical part and NBK couldn't went out at the way it did, without it. Both are responsable, both wanted the same and both wanted to produced the same damage and legacy, their personalities together could go on with the plan as it was in their fantasies and I don't think that the final product could happened like it did if Eric would act alone or Dylan or one of them with another person
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The most terrifying fact about the universe is not that it is hostile but that it is indifferent; but if we can come to terms with this indifference and accept the challenges of life within the boundaries of death — however mutable man may be able to make them — our existence as a species can have genuine meaning and fulfillment. However vast the darkness, we must supply our own light