Many aeons ago, on a small planet, there lived two separate species. One called themselves "the people from/of/owning (much is lost in translation) the planet". The title was often shortened to "Irken", after the planet in question.
The other species preyed on the Irkens. They had no name, no grand designs, no pretensions, not much of anything. They didn't even have solid forms. They lived in the shadows, hunting in groups, earning themselves the moniker of "shadowy pack hunters", or "spith" as one aspiring Irken shortened the name to. Feeding not only on the flesh and blood of the Irkens, but also on the fear that they caused in the smaller, less malleable species.
Eventually, though, the Irkens grew more civilised. They developed first fires, then artificial lighting to destroy the shadows that the creatures lived in. They then developed first ways of repelling the monsters, then ways of destroying them altogether. In time, the once feared creatures became stories told to the children as a way of scaring them into submission.
Eventually, the last few remaining spith were forced further and further away from civilisation, and given less room as the civilisation expanded to cover the whole planet. This continued on until the only way they could survive was to leave the planet, and go somewhere unexplored, that no Irkens would ever go to, or even hear of.