Star Trek: 10 Alien Encounters Before First Contact
7. The Preservers - The Paradise Syndrome
The Preservers were peaceful people who traveled through the galaxy, rescuing those civilisations that they felt were at risk of extinction. Starfleet discovered evidence of this when they visited Amerind, a planet many light years away from Earth, only to find that people resembling the Native American tribes dwelling there.
Spock was able to discover, through the Obelisk left behind by the Preservers to protect the planet, that these were the descendants of Native Americans who had been taken by the Preservers, comprising elements from several different tribes.
Though the Preservers themselves do not make an appearance in the episode, writer Ronald D. Moore felt that the alien race who had seeded the galaxy billions of years previously may have been the Preservers - even though they were said to have vanished many millions of years before the first Native tribes began to arrive in North America. Still, various beta canon sources have confirmed that they are the same.
The Obelisk itself served to protect the planet from such disasters as asteroids and the like, with another such Obelisk being found on a moon of Andoria.