"Sky Spirits" was the name given by the Native American tribe known as the Rubber Tree People to a race of aliens from the Delta Quadrant who visited Earth around 43,000 BC, imparting a genetic bonding to ancient Humans and giving rise to many Native American tribes.
Visiting Earth on a journey which took them more than two generations, the Sky Spirits encountered a small group of nomadic hunters. Although the hunters possessed no spoken language or culture beyond the use of fire and stone weapons, they did have a respect for the land and other living creatures which deeply impressed the Spirits. The Spirits decided to bestow upon the hunters an inheritance, a genetic bonding so the hunters might thrive and protect their world. On subsequent visits, the Spirits found that their genetic gift brought about a spirit of curiosity and adventure, which impelled the Humans who received the gift, whom the Spirits referred to as "the Inheritors," to migrate away from their cold climate to the North and South American continents over the course of nearly a thousand generations. Eventually, they numbered in the hundreds of thousands, but thousands of years later they were decimated by invaders from other lands. Those who survived scattered, many seeking refuge in other societies. When the Sky Spirits eventually returned in the year 2252, they found no signs of the Inheritors' existence.
In 2372, the USS Voyager discovered the Sky Spirits' homeworld in the Delta Quadrant. At first the Spirits hid themselves, believing that the Humans came to conquer them as they did the Inheritors. Using advanced cloaking and weather-control technology, they attempted to halt Voyager's landing. The Spirits eventually revealed themselves, however, when Voyager's first officer, Commander Chakotay, himself a descendant of the Rubber Tree People, was able to contact them and assure them of their peaceful intentions. (VOY: "Tattoo")
- No Sky Spirit characters were ever assigned names in canon productions.