The Avatars

It is not yet known whether The Avatars are a force of Good or Evil as they seem to use both sides to their advantage,
still not much is known to The Charmed Ones about The Avatars,
except that they were led to believe that they could rid the world of evil effectively creating a Utopia. The Charmed Ones agreed to help The Avatars create this so called Utopia after Phoebe had a vision of her future self living in this Utopia The Avatars claimed to make possible. Sadly It was discovered that the Utopia they had hoped for came with consequences and ones that they were not able to live with so rather than vanquish The Avatars they made them restore the world back to how it was before the Utopia began. 
The Avatar's left but not before telling the Charmed Ones that they were not ready to understand what sacrifices had to be made but that one day they would be. 

We the audience have come across The Avatars before as they managed to get Cole onside, but Cole foolishly abused his new found power to re-write history in order to wipe Paige from existence leaving him back as Belthazor and digging his own grave when Phoebe finally vanquished him. How Cole re-wrote history and the fact that he became an Avatar is still un-known to The Charmed Ones.