Gorgan

Gorgan was a malevolent entity from another dimension. Approximately one million years ago, 0, with Q's assistance, used the Guardian of Forever to bring Gorgan, The One, and (*) into the Universe. The group committed many atrocities, including the destruction of the T'Kon Empire. (TNG novel: Q-Strike)

After the Q Continuum banished 0, Gorgan hid himself in a cave on Triacus. In 2268, he was freed by members of a Federation colony, which he then destroyed, sparing only the children. His plans to use the children to conquer the universe were thwarted by James T. Kirk of the USS Enterprise. (TOS episode: And the Children Shall Lead)