- "This is what assault looks like! One more word out of any of you and I'll have you banished! I mean you, too Mercer! Everyone back the fuck off!"
- —Sebastian to Mercer along with Michonne and the group.[src]
Sebastian is shown to be a spoiled self-entitled man, believing that he is better than everyone else and looks down at everyone like they are lower than him. With his mother in charge of The Commonwealth he uses that as leverage to get away with his behavior. Sebastian also shows that people should be grateful to him, as he believes that he is making the commonwealth safe.
Nothing is known about Sebastian's life before or as the outbreak began. He may have lived in or near Ohio.
Sebastian is first seen with Kayla outside the Commonwealth. Their encounter is interrupted by Mercer, who steps in to save them from a roamer. He later complains to his mother about his lack of privacy.
Sebastian will later meet with Eugene's group and tries to flirt with Yumiko. Yumiko turns him down causing Sebastian to get rough with Yumiko, he then shoves Magna to the ground. Enraged, Princess tries to attack him. Outraged, Sebastian orders Mercer to kick them out. Elodie then tries to help Sebastian up, which causes the latter to slap her, much to Michonne's anger.
This list shows the victims Sebastian has killed:
- Possibly numerous counts of zombies
Little is known about their relationship, but Pamela is shown to care enough about her son to have a soldier guard him at all times, much to his dismay.
Mercer the bodyguard of Sebastian. Despite saving his life from walkers, Sebastian is shown to be verbally abusive towards Mercer for ruining his date. Mercer hates Sebastian strongly, but holds his tongue when around him. Mercer also believes there is no reason to kill him as he will likely get himself killed. It's possible that Sebastian looks at Mercer as well as the other solders as expendable.