Titan first appeared in FFIII as a summon before becoming a boss fight (and then later summon) in FFIV when a young Rydia summons him to battle against Cecil & Kain. He then returns in IV the After Years when summoned by an unknown enemy who bares a striking resemblance to Rydia. Titan then returns to his role as a boss for FFV where he once again must be defeated to be used as a summon. Skipping VI, Titan appears again as a summon in the form of Materia in FFVII with an attack that literally pulls the ground from under an enemy and flattens them. Titan would then move on to appear next to Fenrir in FFIX assisting the summoner Eiko.
As the Avatar of the Earth Element for Final Fantasy XI, Titan would become a powerful ally to Summoners with his ability to grant the party increased damage resistance. It was here Titan would be given a back-story where he was once part of a tribe of giants who fell during a battle against a neighboring enemy. One day a young girl named Daemdalus would stumble across the weakened Titan, befriending the fallen giant. When the city found out about this discovery they decided that the giant needed to be executed to protect the city and it's people. In a desperate attempt to save Titan, Daemdalus threw herself in front of Titan to protect him. Watching the from the heavens, Altana summoned both Daemdalus and Titan's souls into heaven and blessed Titan with the power of the Earth. Thus becoming the Earth Celestial Avatar we know now. Daemdalus was also transform into a star and placed in Titan's constellations.