Thi-Sen was a Talz male who held the position of chieftain for a Talz tribe residing on Orto Plutonia during the era of the Clone Wars. During this time, both the Galactic Republic and the Confederacy of Independent Systems dispatched forces to Orto Plutonia. The battle droids of the Confederacy launched an assault on the Talz. In response, the Talz retaliated by attacking both the droids' base and a Republic listening post that was unfortunately situated in the crossfire, resulting in no survivors. These attacks drew the attention of the Republic, prompting them to deploy a task force led by Jedi Knights Obi-Wan Kenobi and Anakin Skywalker, along with Pantoran representatives Senator Riyo Chuchi and Chairman Chi Cho, to conduct an investigation.
Obi-Wan and Anakin discovered that Thi-Sen and his tribe were responsible for the attacks, motivated by a desire to be left undisturbed. Subsequently, the two Jedi Knights facilitated a meeting between Thi-Sen and Cho to attempt to negotiate a peaceful resolution. However, Cho, displaying arrogance, declined to negotiate and instead declared war on Thi-Sen and his tribe. This led to a battle between Thi-Sen's tribe and Cho's forces, resulting in significant casualties on both sides, with Cho himself suffering a fatal wound. Following the battle, Thi-Sen and Chuchi successfully negotiated a peace treaty between Orto Plutonia and Pantora, ensuring the Talz were left to live in peace.
Thi-Sen and his tribe maintained a secluded existence on the icy world of Orto Plutonia. As the Clone Wars unfolded, both the Galactic Republic and the Confederacy of Independent Systems deployed a substantial number of troops to Orto Plutonia. The droids encountered the Talz and initiated an attack. Thi-Sen perceived this as a threat to his people, and in response, launched a retaliatory attack on the droids' base. A Republic listening post was caught in the middle of this conflict, with the Talz slaughtering the clones stationed there, and displaying their helmets and the droids' heads on spears.
Later on, Jedi Knights Obi-Wan Kenobi and Anakin Skywalker, who were dispatched as part of a task force to investigate the massacre, encountered Thi-Sen and his tribe. They were informed about the events that transpired and the Talz's desire to be left alone. The Jedi conveyed their peaceful intentions and desire for friendship, subsequently arranging a meeting between the Talz and the Pantorans. Before departing, Thi-Sen expressed his friendship by giving Obi-Wan a bear hug. Thi-Sen's Talz arrived at the meeting in the wreckage of a destroyed Confederate XT Beetle Transport and politely requested that the Pantorans leave their world. However, Chairman Chi Cho, unwilling to relinquish control of Orto Plutonia, labeled the Talz as trespassers and savages, utilizing the protocol droid C-3PO to communicate with them. Thi-Sen reiterated his people's desire to live in peace and requested the Pantorans to withdraw their people from the planet. Cho, rejecting diplomacy, intentionally provoked and insulted the Talz. Thi-Sen warned that war would ensue if the Pantorans did not comply, a challenge that Cho accepted.
With war officially declared, the Jedi departed for the Republic base to urge Senator Riyo Chuchi to contact the Pantoran Assembly and have Cho removed from power. Thi-Sen mobilized his forces and led them against the Pantorans and the Republic. Engaging the clone troopers tasked with protecting the Chairman, Thi-Sen's forces swiftly overwhelmed the Republic troops, fatally wounding Cho and killing numerous clone troopers. As the Talz cornered the remaining clones, Republic reinforcements arrived in LAAT/i gunships. Chuchi, empowered by the Pantoran Assembly to negotiate with the Talz in the interest of peace, arrived and Thi-Sen chose to halt the attack. Chairman Cho, who had been impaled in the back by a spear during the battle, implored Senator Chuchi to continue the fight against the Talz, asserting that it was for the "good" of his people. He was dismayed to learn that his authority had been superseded by the Pantoran Assembly and died soon after. Chuchi, accompanied by C-3PO, approached Thi-Sen and conveyed that living for his people was a greater sacrifice than dying for them. The Senator then offered to cede sovereignty of Plutonia to the Talz, an offer Thi-Sen accepted. The Republic troops departed from Orto Plutonia, and the Talz returned to their village.
Thi-Sen was a skilled warrior, prepared to lead his people into battle when necessary. He possessed expertise in military tactics, reconnaissance, and narglatch riding, all of which contributed to his people's success in destroying the Separatist garrison and unintentionally eliminating the Republic garrison stationed on Orto Plutonia. Thi-Sen's strategies later inflicted heavy casualties on the Republic's clone cold assault troopers sent to the planet to investigate the unresponsive status of the Republic garrison. Thi-Sen was honorable and sought peaceful resolutions with the Pantorans. He initially pursued diplomacy with Obi-Wan Kenobi, Anakin Skywalker, and Chi Cho, but the Chairman's refusal led to the commencement of the One-Day War. Following Cho's death during the battle, Riyo Chuchi extended an offer of peace to Thi-Sen, and the two diplomatic representatives of their respective peoples established amicable relations.