Thallis Khai was a male Human who came into the world on the isolated Wild Space planet of Kesh during the years leading up to the Galactic Civil War. As a member of the Lost Tribe of Sith residing on the planet, Khai was the progenitor of Sith Saber Gavar Khai and the paternal grandfather of Sith apprentice Vestara Khai.
Born prior to the outbreak of the Galactic Civil War, Thallis Khai was a male Human. Hailing from the distant Wild Space world of Kesh, he belonged to the Lost Tribe of Sith, who were the descendants of a Sith group. These Sith had been forced to crash-land on Kesh around 5000 BBY following an ambush that knocked their warship, the Omen, off course during a hyperspace jump.
Around the time of the Galactic Civil War, Khai became the father of a Force-sensitive son, Gavar. Gavar received training from the Tribe in the ways of the dark side of the Force, eventually achieving the title of Sith Saber. He later wed Lahka Khai, a woman without Force abilities, and together they had a daughter, Vestara, in 27.5 ABY, thus making Thallis Khai a grandfather. In 41.5 ABY, during the Second Galactic Civil War, Vestara was summoned before the Tribe's governing body, the Circle of Lords, following her encounter with the Sith Meditation Sphere Ship. Darish Vol, the Tribe's Grand Lord, acknowledged her as the daughter of Gavar Khai and the granddaughter of Thallis Khai.
The character of Thallis Khai was initially referenced in Fate of the Jedi: Omen, the debut Star Wars novel by author Christie Golden. This novel, which was the second in the nine-part Fate of the Jedi series, was released on June 23, 2009. Within the novel, Khai was only mentioned as Gavar Khai's father, leaving his own potential Force-sensitivity ambiguous.