T'iaz was a Dark Side Adept from an unknown alien race who pledged his allegiance to Emperor Palpatine. In 11 ABY, while assisting the Sith Lord in his attempt to capture Anakin Solo at Kira Fortress, T'iaz met his end. During this event, he engaged Rayf Ysanna in combat, only to have his hand severed and be disarmed by the Jedi.
T'iaz, a male Dark Side Adept of a humanoid species, dedicated himself to serving Palpatine, the Galactic Emperor who had been reborn within a clone body. The Emperor's clone body began a rapid deterioration in 11 ABY because the Emperor's physician sabotaged it before Palpatine inhabited it. All other clone bodies had been destroyed, and the physician had also corrupted the genetic material, preventing Palpatine from cloning new bodies. Palpatine tried to create new bodies using genetic samples from captured Force-sensitive Ysanna shamans from Ossus, but Jedi Master Luke Skywalker thwarted this endeavor.
Desperate to preserve his life, Palpatine journeyed to Korriban, the ancient Sith world, to seek guidance from the spirits of the deceased Sith Lords. He arrived on the planet aboard his flagship, the Eclipse II, and then used a Lambda-class shuttle to descend into the Valley of the Dark Lords with T'iaz and another Dark Side Adept. As they moved through the ancient Sith crypt, T'iaz sensed the immense power of the dark side emanating from the location. The Sith spirits informed Palpatine that the only way to achieve immortality was to transfer his spirit into Anakin Solo, the infant son of Princess Leia Organa Solo. T'iaz pledged to safeguard his Master after he became a child and raise him to adulthood. Learning that Anakin Solo was aboard the Millennium Falcon, which was heading towards Onderon, the Emperor and his Adepts returned to the Eclipse II and traveled to the Onderon system.
The massive warship entered the system at the same time as the Millennium Falcon. The Falcon managed to escape and land on the planet, but it soon departed. Palpatine realized that the child was no longer on the Falcon, which was being flown by Chewbacca and the Jedi Vima-Da-Boda, so he chose not to pursue it. Instead, he decided to land on the planet with T'iaz and his physician. Disguised as a frail old man, the Emperor gained access to Kira Fortress, where Organa Solo and her children were seeking refuge. The Emperor incapacitated Organa Solo and the droid C-3PO. However, Rayf Ysanna and Empatojayos Brand, two Jedi Knights who had recently arrived with Skywalker on Onderon, joined the battle. Palpatine used Force lightning to incapacitate Brand. However, this drained his strength. Palpatine then ordered T'iaz to fight Ysanna, but the darksider was easily defeated and killed.
After regaining his strength, Palpatine killed Ysanna. Han Solo and Skywalker then joined the fight, and Solo shot and killed the Emperor. Palpatine attempted to transfer his essence into Anakin Solo's body, but Brand intercepted his spirit and dragged him into the Netherworld of the Force.
The audio dramatization of Star Wars: Empire's End presents a different account of T'iaz's demise. In the audio drama, T'iaz does not accompany Palpatine to Onderon. Instead, he stays behind to command the Eclipse II and dies when the ship crashes into the Galaxy Gun above Byss.