Jack Vessalius

Jack reveals, through his speech when he first possesses Oz, that Glen is still living. Despite this, he says to the Baskervilles that if they wish to repeat the past, then he will once again turn his body into a blade that will destroy the Death Gods.

Recent chapters showed that Jack was Gilbert and Vincent's master. He had picked the brothers from the streets and allowed them to become his servants. Later, when Jack confronted Glenn, it shown that Gil had stepped in and saved Jack from mortal danger, which resulted with Gil's death. This event made Jack guilt-stricken, and he deemed himself a failure in protecting Gilbert. He hopes that Gil will stick with his current master (Oz), but he still thanks Gilbert for calling him "Master" despite of what he had done. Some flashbacks have shown him trying to introduce Gilbert and Vincent with Alice, hoping that they would be her new friends since she has always been alone and the closeness of their age.

His efforts failed when Alice taunts Vincent's red eye and Gilbert pulled her hair in counter. Apparently, he was also aware of Glen's intentions but didn't asked further for the sake of their friendship, a decision he later regrets. (Source: Wikipedia)

It's been revealed that Jack actually caused the tragedy of Sablie by exploiting Vincent's role as the child of misfortune. Jack, with the help of Miranda Barma, tricked Vincent into opening a path to the abyss so that he could have the world be swallowed into its depths. His plan was to bring the outside world to Lacie and keep her from being lonely, but it failed due to intervention by Glen (Oswald) Baskerville and Alice.