Gorgan

Gorgan, the "Friendly Angel".

Gorgan (also known as the "Friendly Angel") was a noncorporeal being preserved in a cave on the planet Triacus.

In 2268, Gorgan was accidently released from his cave by the Starnes Exploration Party. He forced the adults of the Exploration Party to become mentally unstable and commit suicide and manipulated the children of the Exploration Party to follow him in his quest of conquering the universe.

On stardate 5029, Gorgan used the children to establish mind control over the crew of the USS Enterprise and forced the ship on a heading for Marcus XII. Gorgan's hopes were than nearly a million children on Marcus will join the other children as their friends, and the rest will be their enemies.

The children could collectively summon Gorgan by twice chanting:

Hail, hail, fire and snow

Call the angel we will go

Far away, for to see

Friendly Angel, come to me

Gorgan was defeated by Captain Kirk, when he turned the children on him by recalling their lives with, and deaths of their parents. Losing the children's obedience, Gorgan lost his power and dissolved into oblivion. (TOS: "And the Children Shall Lead")

Gorgan was played by Melvin Belli. Curiously, Kirk first spoke Gorgan’s name when he summoned the being. There was no reference to his name, other than "Friendly Angel" prior to that point, which leaves one to wonder how Kirk learned of his name in the first place.