The Titans are a primordial race of divine beings that preceded the Gods. They were the children of Gaia andOuranus, and ruled over the universe after Kronos overthrew their father,Ouranus. Though the story of their rise to power is similar to that of the Olympians, the Titans were for the most part chaotic and corrupt, a fact most evident in their leader, Kronos. Humanity was created during their reign, but though it was called mankind's "Golden Age" it was not a time of peace for them. The Fates thus gave a prophecy that Kronos' tyrannical rule would be overthrown in the same way that he took power, with his children rising against him.
Yet in another version of the myth, people lived in peace in the golden age. They had no locks on their doors, as thievery had not been invented. No one worked; every thing they needed was already there. In this version, Zeus overthrew his father to have power. It was a time of peace in this version (most likely made up by Kronos himself).
Trying to evade the prophecy of his downfall, Kronos devoured each of his sons and daughters as they were born, but his wife Rhea saved their final child, Zeus, by presenting Kronos with a stone wrapped in swaddling clothes instead. Hiding him away from the other Titans, Rhea ensured that Zeus would be raised in secret, and when he was grown he freed his brothers and sisters from their father's belly and stirred up a rebellion against the Titans
The war between the Titans and the Gods was called the Titanomachy. The Gods were victorious and threw Kronos and the other evil Titans into the depths of Tartarus, but spared those that took their side in the war, such as Helios and Prometheus, and gave them places in the new order. Those Titans that took a neutral stance in the conflict, like Oceanus and several of the Titanesses, were left alone, though many of their roles were taken over by Olympian gods.
The power of the Titans is far superior to that of the gods as Kronos stated that the Olympians would fade soon after the destruction of their thrones. The Titans however had their entire mountain fortress on mount Othrys destroyed millenia ago yet they have retained enough power to lead a war against the Olympian gods (which they almost won), showing that the gods are weaker then their predecessors.
According to Dionysus, a Titan's true divine form is so powerful that mortals are incinerated by being in their very presence (or that may have been Kronos' alone).
The Titans had complete dominion over the very elements light, time, space, earth, air, water and fire and most likely 'gave birth' to the things they preside over (e.g. Selene & Helios being the Moon & Sun instead of a deity of the moon and sun like Artemis and Apollo).
Some Titans possessed the ability to release an incredible wave of force (or energy), usually accompanied by a scream.