Story
Terra spends his days as a Keyblade apprentice training under Master Eraqus at the Land of Departure along with his friend, Aqua. Terra's long-time dream was to be a Keyblade master like Eraqus.

A few years ago, Master Xehanort, whom Terra did not recognize, visited the Land of Departure, and brought with him Ventus, a young boy that Xehanort asked Eraqus to take care of and train to be a Keyblade warrior. Terra greeted Ven and asked him who he was. After Ven answered and he called Aqua over to them, Terra proceeded to ask him several more questions, including where he came from and why he was there. However, Terra was terrified to see Ven cry out in agony, then fall to the floor. Terra felt a great amount of guilt, believing that it was his fault that Ven became comatose.

After a few days, Ven woke up from the coma. Wanting to make it up to Ven, Terra befriended him and became his sparring partner. After a long day of training, Terra told Ven and Aqua about his dream of being a Keyblade master, which was also Aqua's dream. Terra smiled, and gave Ven his wooden sword, saying that he, Ven, and Aqua, all carry the same dream. Ven had been Terra's best friend ever since.

The three spend time together whenever possible, realizing each others dreams and even distributing good luck charms that would always keep them connected.

Years later, he takes the Mark of Mastery Exam alongside Aqua in order to become a master, but is unable to become one, as he is unable to control his darkness. Unbeknownst to them, Master Xehanort is responsible for the appearance of such darkness during the Exam.

Terra was even more surprised to find out that he held darkness in his heart, which cost him a chance to be a Keyblade master. Later that day, he was approached by Master Xehanort, who told him that despite the darkness being in his heart, it didn't mean that it would be a problem. Instead Master Xehanort tells him that darkness cannot be destroyed as Master Eraqus said, but it can only be channeled.

Minutes later, Terra is sent on the quest to find a missing Master Xehanort and stop the threat of mysterious creatures called the Unversed with a promise that Master Eraqus may reconsider him as a Keyblade Master. Aqua is later consulted and told to watch over Terra, as he may be tempted by the darkness.

While on his journey, the darkness in Terra's heart catches the attention of the evil denizens of the worlds he visits. One is Maleficent, the evil witch taking control over Terra through his darkness and causing him to steal a sleeping Princess Aurora's heart. This action, as well as the many others the dark residents of the other worlds would request of him, would haunt Terra for the rest of his journey, even if his reward was more information on Master Xehanort's whereabouts.

Terra's quest through the worlds eventually brings him to the Radiant Garden, where he witnesses Master Xehanort heading in an unknown direction; assuming there may be some new information for him, Terra follows him. As Terra treks through the world, a battle with a massive Unversed leads him to reunite with Aqua and Ventus. After discovering that Ven had encountered the enigmatic Vanitas, Terra urges the boy to go home, as urgent duties Terra needs to fulfill will make the situation unsafe.

Aqua, thinking these duties are not as Master Eraqus had assigned them, is quickly told by Terra that his goal is still to destroy the darkness, to which Aqua counters by stating the fact that Terra seems to embrace it. Ventus quickly comes to Terra's defense, Terra angered when he discovers Master Eraqus had asked Aqua to spy on him, thus learning of his master's mistrust. Infuriated and hurt, Terra turns a deaf ear to Aqua's pleas and attempts to reason with him and departs. Terra soon comes to believe that he can only rely on Master Xehanort.

Terra soon locates Master Xehanort in the underground catacombs below Ansem's castle due to Braig, the elderly Keyblade Master seemingly having been captured by the man. Braig battles Terra in an attempt to obtain the Keyblade, with Terra unable to retaliate due to Braig's dirty tactics. However, some quick encouragement from Master Xehanort gives Terra the strength to fight back.

After the battle, Terra gains the upper hand by using his anger as a weapon, thus losing control of his darkness, scarring Braig's cheek as well as ridding the man of his eye. Braig fleeing as he reels in pain, a freed Master Xehanort soon approaches Terra, who is shocked to find he has been controlled by the darkness yet again. Master Xehanort attempts to have Terra see things in a different light, that he has controlled the darkness rather than vice versa. Terra refuses and states that now he has no home to return to at the end of his journey.

Master Xehanort then proceeds to offer Terra a position as his pupil, causing him to doubt Master Eraqus. Master Xehanort then explains how darkness is always born within the light, revealing that fear is why Master Eraqus failed to pass Terra in his Mark of Mastery Exam. Master Xehanort then begs Terra to join him in bringing balance to the worlds, stating their mission is to defeat the darkness that upsets the balance, Vanitas. Master Xehanort then pulls the final string, acknowledging Terra's long-time wish and calling him "Master Terra". It is because of this that Terra comes to know Master Xehanort as his new master. As Terra prepares to leave the Radiant Garden, Ventus catches up with him, asking to come along on Terra's journey, to which he refuses. Terra does say, however, when Terra really needs him, he knows Ventus will be there.

In Olympus Coliseum, Terra meets Hades, upon their meeting, Hades references the meaning of his name in Latin by saying "Kinda earthy." Hades later convinces Terra to join the game, in which he (Terra) encounters the darkness-controlled Zack. Terra emerges victorious and leaves the world.

In Deep Space, however, when Experiment 626 steals the good luck charm that Aqua made for him, Terra's pleas for 626 to return it, which in turn forces him to realize just how much he still cares for Aqua and Ventus.

Some time later, Terra finds himself encountering a warm light which calls him to another world. Discovering Paopu Fruit growing on the island, he recalls his friends and the distribution of the good luck charms at the beginning of his quest, Terra wondering why he is there and if he'll ever see Aqua and Ven again. Soon laying eyes upon a young Sora and Riku, he discovers Riku's potential and holds a conversation with the boy. Terra asks why he wants to go to other worlds, later choosing Riku to be his successor when he is able to hold the Keyblade. Riku stating countless times he has cherished things to guard, Terra then makes note that he still has things to protect, as well.

Called soon after to the Keyblade Graveyard by Master Xehanort, Terra learns from the man that Ventus has learned the truth about his past, has gone back to see Master Eraqus about it, and now has a high chance of being eliminated. Terra immediately returns to the Land of Departure, arriving just in time to save Ventus from a would-be fatal attack by Master Eraqus. Refusing to obey Eraqus' orders to stand down, Terra taps into his darkness. After throwing Ventus into a portal to another world, Terra soundly defeats Master Eraqus, but immediately regrets this action afterwards. However, Eraqus insists that he had failed Terra, and he himself must be tainted by darkness to have raised his Keyblade against Terra and Ventus in the first place. At that moment, however, Master Xehanort arrives and murders Master Eraqus in cold blood as Terra looks on. With his true intentions exposed, Xehanort beckons Terra to come to the Keyblade Graveyard before shrouding the Land of Departure in darkness, which leaves it in ruins.

Upon arriving at the Keyblade Graveyard, Terra meets up with Aqua and Ventus. Terra explains what happened to their master and admits that he did have to be watched, vowing never to go astray again. However, Aqua warns him that darkness is based on hatred and rage, and that if Terra had come for revenge, then Xehanort has already won. In the ensuing fight with Master Xehanort and Vanitas, Terra succumbs to his darkness once more and battles the elderly man, who makes note of the χ-blade's creation before unlocking his heart and possessing Terra's body, thus forming the new Xehanort, while Terra's mind goes on to find residence within his discarded armor as the Lingering Will. Despite the possession, Terra's heart fights back against Master Xehanort's several times, which leads to the new Xehanort unlocking his heart once again to retaliate, leading to Xehanort's amnesia.

Personality
Terra's calm and cool exterior hides a heart that would fight for his friends, yet he is constantly tempted by the darkness, similarly to Riku. Oblivious to the fact that Master Xehanort is attempting to seduce him into darkness, he is forced to doubt those most special to him, and only realizes his wrong-doings after they occur. While not gullible, Terra can be overly trusting, which most villains use to their advantage, leading to his misadventures. His experiences with darkness bring a negative vibe to him, but Terra holds his bond with Ventus and Aqua in high esteem, willing to fight for them despite his ties to the darkness, wishing to help them long after his possession. This is seen with both the new Xehanort and the Lingering Will, both instances of Terra's faded consciousness acting on Ventus's and Aqua's behalf. He also holds Master Eraqus in high regard, viewing him as a surrogate father, which he proclaims to Xehanort, and also cries at his destruction.

Appearance
Terra is a tall young man with brown hair that reaches to the base of his neck in the back and is styled into rather messy, vertical spikes and bangs that frame his face. He has blue eyes and slightly tanned skin. Interestingly, he bears a slight resemblance to a young Xehanort, save for the color of his hair, skin, and his eyes.

Like his friends, Terra wears two intersecting straps over his chest, though his red ones are rather different, dropping much lower down and almost resembling criss-crossed suspenders. Also unlike Aqua and Ventus, Terra does not wear his badge (which is gold as opposed to the others' silver) on these straps. Instead, he wears it on his belt. He wears a skintight, black, high-collared shirt, showing that he is rather muscular. Terra's pants bear a distinct feudal Japanese style; his belt is tied like an obi-sash and he wears hakama (traditional samurai pants distinguished by the large pleats). His hakama are dark grey near the top, with several loops for his belt and two buttons, both of which are undone. The rest of the pants are tan with a small, lighter stripe of tan on the bottom hem. Terra wears a plain black wristband on his right arm, while his left arm is significantly more armored.

Like Aqua and Ven, Terra wears armor on one arm, with his bearing similarities to both of his companions. Terra's armor shares the large, ornate crest (colored gold) with Ven and the long, segmented section (each segment alternating between dark grey and dark red) with Aqua, though Terra's is much longer, reaching all the way to the bottom of his hand. He also wears a black, fingerless glove on his hand and what appears to be a black gauntlet on his forearm, over the segmented armor, which also has small pieces of dark red armor on it. Finally, his armored boots are dark brown and gold.

By touching the armor piece on his arm, Terra will become fully clad in armor. When in his suit in "Birth by sleep", Terra is clad from head to toe in armor, mostly in shades of dark brown, gold, and red. Dull orange lines decorate the armor as well. Notable additions to his armor include upturned, sharp red hooks on the backs of his boots, a navy blue cape, and a dark-visored helmet. His helmet sports two tall, red prongs on either side. In Kingdom Hearts Birth by Sleep, his armor is now slimmer, the colors on the armor are much brighter, and the cape is omitted. The dark brown is now shown to be black, as is the visor of his helmet.