First beginning based off the Malaysian myth, a spirit created by warlocks and murderer's blood which was used for their own benefit, the Polong has had many steps in its development. Abilities, story, art, etc. all have changed and grown.
One more interesting note is that the Polong was originally an it, without a gender. But to make a VO easier, make him easier to connect to, and give him more of an identity I went with a male personality and association.
Finally, while I doubt most will care, the Polong's development name was Ethereal Hopper.