Future (1st timeline)
Unknown but assumed dead in the first part of the tutorial as Hansoo has no major memories of this person.
Past (Common to both timelines)
In the same college as Kang Hansoo
Present (2nd timeline)
Became Kang Hansoo's cleaner, works in the shadow while Hansoo is exposed in the light.
In the first part of the tutorial he decides the only way he'll be useful to Hansoo is by taking care of the people causing problems for Hansoo. The first cleaner work he does is causing people trying to interfere with Hansoo's fight in the Altar to get knocked in and eaten by the Carnivorous Beast.
Hansoo has Sangjin collect the runes and artifacts secretly left behind by Miyamoto, one of which is the rank 8 skill Lord of the Dead. He uses these abilities to kill of the clansmen that are attempting to take Hansoo's acquaintances hostage.
It's later revealed that at some point in time Sangjin also holds the daughter of Wongyung, the Dark Mad Lord, hostage in order to get Wongyung to listen to the orders of Sangjin.
At start of the zone he forcefully subdues 4 of the Seven Departed Souls and gets them under his control using Wongyung's Lord Trait. The ones he gets under his control are Arc Mariangt, Kyle Cooper, Tina Charliz, and Yoruba.
None currently revealed.