The Titans (Greek: Τiτᾶνες, Titânes - "Straining ones") were members of the second generation of immortal beings in Greek mythology. Though many beings were referred to as Titans in the myths, the term is usually used in reference to the twelve children of Gaia and Ouranos.
They ruled the cosmos prior to the Olympians, with whom they fought for control of the universe in a series of battles known as the Titanomachy. The Olympians emerged victorious, as many of the Titans were cast into Tartarus.
The first generation (Ouranides) change
The second generation (Coenides, Creonides, Hyperionides, and Iapetionides) change
The second generation of Titans were mostly children of the original Twelve. These include the children of Okeanos and Tethys: the Potamoi, gods of rivers, and the Okeanides, who were three thousand in number, as well as the Nephelai, cloud nymphs.
Last but not least were the children of Krios and Eurybia (daughter of Gaia and Pontus): Pallas, Astraeus, and Perses, the latter of whom would go on to marry Asteria, with whom he sired Hecate, goddess of magic and witchcraft.