
Overzealous in his goal to save Senna, Lucian refused to turn back, but his decision cost him Senna's life as she sacrificed herself to save him from an oncoming attack from Thresh. Many years later, Thresh encountered Lucian and Senna, a married couple of Sentinels of Light, in a forbidden Helian vault in search of a cure for the latter's curse. He roamed the Shadow Isles killing people and imprisoning their souls within his lantern, becoming known in the folklore of Runeterra as a bogeyman figure. As decades passed, Thresh's spectral form morphed into a reflection of his darkest traits.

Grael embraced his transformation and took on the moniker Thresh, eager to act out his desires for cruelty without punishment or the limits of mortality. Isolde's resurrection failed and caused a blast of magic that corrupted the Blessed Isles' protective mist into the Black Mist, turning all of the inhabitants into wraiths. Grael delighted in the carnage and suffering that ensued, and took it upon himself to lead Viego to the Waters of Life. When the monks refused, Hecarim and his knights took the opportunity to slaughter the monks and all of the natives. One day, a fleet of ships from Camavor invaded the Blessed Isles, led by their king Viego whom wanted to use the Waters of Life to resurrect his wife Isolde.

Angered, he believed that Rastofir was trying to steal his research for his own benefit, so he arranged Rastofir to be killed by a miscategorized artifact so he could manipulate the order into a pragmatic direction. Grael kept the tome in his possession, but his superior, Head Warden Rastofir, stopped him and threatened to demote him.

Growing frustrated over his fellow wardens getting killed by the artifacts, he took interest in a nameless tome claimed to whisper one's darkest thoughts. After years of working in the vault, Grael grew bitter and cruel. Grael felt bitter towards his new position as he believed himself more gifted than his noble-born peers who got more prestigious roles, and that his lowly position would stop him from being recognized. He served in the order for many years, expecting to be recognized among Helia's masters, but due to his humble background he was delegated to work as a warden to safeguard Helia's magical artifacts which he took as an insult. The wraith Thresh was born in the Blessed Isles as Erlok Grael, a monk of Helia.
