Thomas Aquinas, Compendium of Theology

From this it appears, further, that God alone can be Creator. For to create is the prerogative of that cause which does not presuppose another cause that is more universal, as we saw in the preceding chapter. But such causality pertains to God alone. He alone, therefore, is Creator.

Besides, the more remote a potency is from act, the greater must be the power that reduces it to act. But whatever distance may be imagined between potency and act, the distance will ever be still greater if the very potency itself is withdrawn. To create from nothing, then, requires infinite power. But God alone is infinite in power, since He alone is infinite in essence. Consequently God alone can create.