Kukulkan

Kukulkan was the last of an ancient serpent species who visited Earth's distant past.

A being of immense power, Kukulkan came from a race that was spacefaring and powerful before humanity ever discovered fire on Earth. As the last of his race, he traveled to Earth to teach peaceful ways, so the civilizations there would not go the way of his own once-destructive civilization. With an appearance that resembled a dragon (green snakelike face, yellow eyes, a single pink horn, blue feathers and wings, and a serpentine red and pink body), Kukulkan became known as the "winged serpent god," and was respected for the knowledge he brought.

He was instrumental in the technological and architectural advances of the Egyptian, Mayan, Aztec and South Asian civilizations. He also taught them new techniques in art and agriculture, with the hope that they would combine this knowledge to complete Kukulkan's city and live in peace. Unfortunately, this did not happen, and the end goal of becoming an energy amplification system (used as a signaling device to summon Kukulkan)
did not come to fruition.

When he left Earth, he promised to return when summoned, but that never happened. So instead, he traveled space, collecting peaceful specimens for his intergalactic zoo.

In 2270, he sent a probe to Earth, which was investigated by the Enterprise.

He became angry when he found out humanity was more brutal and warlike than he had anticipated. When Captain Kirk and his crew encountered Kukulkan, he trapped the vessel, and tested the crew to see if they should be destroyed.
Luckily, the Enterprise crew were able to convince him that his "children" were grown, and seeking peace in their own ways. Kukulkan departed, still forlorn, but with the knowledge that his long-ago teachings may have helped humanity after all.

Kukulkan's ship is surrounded by an energy field that projects a holographic image of a winged serpent.