The Titans were the original 12 gods of Greek mythology prior to the rise of the 12 Olympians and consisted of the many children of Gaia and Uranus - led by Cronus, they were primal forces that were often depicted as giant and fearsome.
The Titans engaged in a large war with the Olympians that ended with the Titans being defeated and many of them being cast into Tartarus as enemies of the gods, they were one of the few beings in Greek mythology that were said to rival the power of the Olympians.
Before their war with the Olympians the Titans had war with their father Uranus Gaia wanted her husband to be punished for what he did to her other children the hundred-handed giants and the Cyclopes. The titans followed Gaia and Kronos commands they wanted him to pay for the things he had done but they also wanted to take over what he ruled. After the war Gaia was upset that Kronos and the other titans left their other siblings in Tartarus.
Their father Uranus feared a prophecy that one of his children would defeat and his rule over the earth would end. The titans had that same fear when a prophecy about one of Kronos children ending their dominance over the earth this action would lead to the war between the Titans and the Olympian gods. Zeus was the one who make what the titans feared come true after he freed his siblings from his father. During the Titanomachy all of the male titans fought the Olympians while most of the female titanesses stay out of the battle. To when the war Zeus freed the Giants and the Cyclopes who were feared by their siblings and father after the battle the suffered the fate as their siblings.
After the along fight the Olympian deities took the titanesses as wives the gods married their own family members. They were all upset about the fate of their husbands Asteria Hecate's mother was so upset that she changed into an island to escape from Zeus who lusted for her and tried to force her to love him. While all the first generation male titans were imprisoned Atlas and a few other titans suffered the worst fate of all holding the weight of the sky or world on their shoulders to keep their parents separated.
Coeus, Hyperion, Iapetus and Crius were the first titans who were forced to hold up the sky and we're called the four pillars of the world. However the burden of holding up their father's body ended after the four were tossed in to the pits of Tartarus making Atlas carry the weight alone. While most of the titans were prisoners in Tartarus and some forced to hold the sky in some myths or hold the world in some myths a few help the Olympians or stayed out of the war. Not all of the titans survived the war some were killed by their own children and some killed by the Olympians.
Though the titans fought against the Olympians some of them stayed out of the war or helped the gods those titans were the second and third generation titans. Imprisoned the titans still coused trouble Atlas using, tricking and lying to Hercules so the demigod could take his place and the titans attacking a young Dionysus. Despite the fact that the titans and Olympians didn't get along Zeus has offered them freedom in one myth if they help the gods the only problem was when they were freed the Olympians and titans starting fighting all over again the lost again and were thrown back into Tartarus.
In the myth about the titans and Dionysus Hera had them eat the young god and action that made Zeus angry. The god of thunder fought them to free Dionysus and the titans were punished again. Though Gaia was angry about what her husband did and her titan children did the primordial earth goddess wanted the Olympians to pay for what they did and sent the giants to fight the starting the Gigantomachy war between the giants and gods. The Gigantomachy was revenge for what happened to the titans in the Titanomachy.