The Avatars are personifications of the Gems of Chaos, created with them near the end of the first Cycle. The gems were imbued with the essences of the seven incitors of the original Cycle, and with them the combined powers of every human being currently on the planet, and were later modified and butchered by the Creator himself into forms he could more accurately predict and manipulate to his needs. As such, a standalone Avatar is essentially a single-dimensional personality that revolves around one vauge and generic motive, and they follow it blindly and recklessly if left alone. It is extremely rare for them to be able to actually accomplish anything on their own, however - they are symbiotic in nature, and require a host that is sympathetic to their motives to control.
Once an Avatar has contacted a host suitable to them (usually by way of said host physically holding their gem of residence), they take control of the host's body by force. Their previously one-dimensional personality is bolstered by the personality traits of their chosen host, filling in the gaps and starting to communicate and interact like any other ordinary sentient being (with the exception they are still extremely focused and obsessed with that one motive they're imbued with). While it's not unheard of for an Avatar to commune with and even share roles with its host, most of them shut them out of their own body entirely and left simply to watch the Avatar do things beyond their control.
There are seven Avatars in all, each corresponding with a Gem of Chaos:
Combat, the Red. This Avatar prides itself on fighting ability, and seeks out hosts who share similar pride in their combat potential, or desire such power but do not yet posess it. It is very rare for a person of good will to be used by the Red, and even then, they fight a constant uphill battle to maintain control of their power and avoid hurting innocents in the process.
Vengeance, the Blue. This Avatar sympathises with those who have been inflicted a grevious wrongdoing, and offers opportunities to get even and punish the ones resposible. Most hosts linked to Blue are very easy to motivate and usually relinquish control willingly when offered the chance at revenge. Blue has possessed a very wide variety of people, but all are connected loosely in that a certain tragedy befell each and every one of them in which one or more people could be directly held accountable.
Knowledge, the Purple. This Avatar seeks simply to learn and teach. Strangely enough, it actively avoids people who are already knowledgable for the most part, but instead seeks out individuals driven by the need to discover a certain range of information but have yet to do so. Many Purple hosts are peaceful in nature and mind their own business in the pursuit of knowledge (and as such, researchers such as scientists and historians are common targets), but often Purple will stumble apon a host that is required to fight to find and keep information, or is wanted dead for the reason that they know something they shouldn't.
Compassion, the Yellow. This Avatar acts not out of benefit for himself, but out of care for his peers. Yellow will typically join with a large gathering of people, earn their respect and do everything it can to ease their burden and fulfill their goals. Yellow's hosts are frequently figures of authority and leadership for this reason, but it's not uncommon to see it as an overly supportive civilian, or an individual hopelessly in love with another individual rather than a crowd, or even for it to assist its community regardless of whether or not they even approve of its host's methods. Yellow can be especially dangerous when given a position in a militaristic group or a mob with a pack mentality.
Dominion, the White. This Avatar is practically the polar opposite of Yellow - while Community works in tandem with its peers and seeks their general approval and praise, Dominion seeks to have the last say in everything and desires nothing more than complete and total control over everything. While some motives can also cross over with Red's, White is different in that he doesn't seek power just for the sake of being powerful, but rather to opress others with it. As such, White's hosts are almost universally evil in the first place, or turn evil very shortly after meeting the Avatar.
Chaos, the Green. This Avatar seeks to be the embodiment of Chaos itself - spontaneous, unpredictable and just all-out nutty. There is almost no pattern to what Green desires to accomplish, what hosts it chooses or what repercussions it has on those around it, though it has been known to hover very loosely around individuals who were in some way mentally unstable to begin with. What happens when Green comes to light is anyone's guess - it has successfully created anarchy just as much as it has created mass ecstacy and joy, but the general rule of thumb is, as long as things are quiet, stable and boring, Green seeks to change it.
Justice, the Cyan. This Avatar is a vigilante - a protector of the weak and innocent, and persecutor of the strong and guilty. Cyan seeks simply to stand for what is right and punish others who don't follow suit. His specific methods, however, are tailoured to his host of choice - Cyan is obviously popular with budding superheroes, but they themselves aren't always generous with how they deal with their problems and sometimes end up being ostracised and even hunted down by the very people they had been so determined to protect.
Once an Avatar is bonded with a host, they almost universally remain until death (though sometimes they sever their own bonds with their host if the Avatar feels they weren't the most appropriate choice in hindsight). The Creator designed their existing personalities in such a way that they are practically destined to clash with each other and many others around them, to such an extent that it inspires global chaos and ruin no matter what. The Avatars and their hosts are also made extremely powerful because their gems imbue them with high-level Chaos Control, but due to preconceptions they all develop apon waking up, almost none of them ever realize their full potential. Once a successful Cycle is completed (almost universally resulting in the death of their hosts through various but expected reasons), the Avatar is drawn back into their respective Gem of Chaos and held there until they are needed to start another Cycle - by which point several millennia will have passed, and resulting in the Avatar forgetting a significant portion of what they even accomplished in their previous roles.