|Appeared in|| Arrow: Three Ghosts|
Sebastian Blood, also known as Brother Blood, is an alderman and undercover cult member who rose to power following the Undertaking.
Sebastian was getting regular reports from Daily about movements conducted by three people looking into one of his test subjects, Maxwell Stanton's death. Sebastian gave Cyrus Gold locations of where to strike; Queen Consolidated's applied sciences division and a blood bank which were necessary for making more Miracle.
Sebastian learns from Daily that the police are planning to go after Cyrus Gold and sends Cyrus to confront them. Meanwhile, in his civilian guise, he romances Laurel Lance, taking her Christmas shopping, and announces his campaign for mayor of Starling.
Sebastian has his subordinate inject a captured Roy Harper with The Miracle. When The Arrow appears, Sebastian orders Cyrus to kill him; Cyrus is defeated and Sebastian flees. He meets with Slade Wilson, who is revealed to be Sebastian's employer and the true mastermind behind the Blood Cult.
After Moira is murdered by Slade, Sebastian officially becomes mayor of the city. Sebastian later attends Moira's funeral reception where Laurel becomes suspicious of him again as he became mayor just after Moira's death. Sebastian was contacted by Slade when he was settling into his new office and told him to remember who he was still working for, and was later visited by Laurel claiming to need help with a case but secretly bugged his computer. Laurel later with Quentin and Kelton discovered that Sebastian had written a condolence letter the day before Moira died and Laurel told Oliver, now aware that he was Arrow, that she was right. Later Oliver personally met with Sebastian to tell him that he is the Arrow and tries to understand Sebastian's motives and he explains that Slade will destroy the city with his army and the people will be in a time of chaos and fear, so they will turn to Sebastian for guidance and he will lead the city into a new age. Later Sebastian wore his mask to talk to Slade's army unaware that Oliver and Diggle were rigging the place to explode. Brother Blood told the troops that they will become a vital part of the Starling's future.
While Starling City was being destroyed, Sebastian was perfectly calm, until one of Slade's soldiers snapped Kate Spencer, the district attorney's neck. Sebastian immediately goes to Slade and complains about what happened, only for Slade to say that he is going to reduce Starling City to rubble. Sebastian then steals the cure of Mirakuru from Slade, and brings it to Oliver. He says that the mask he wore was the image of his father that gave him nightmares every night and he created it to overcome his fears. He says that when the destruction is all over, he will try to bring Starling City into a new era. When Oliver states that the people would never accept him after what he has done, Sebastian says that if Oliver exposes him, he will expose Oliver. Oliver then leaves. Later, Isabel approaches Sebastian. After realizing that Sebastian gave away the cure for Mirakuru, Isabel kills him.
- Oliver Queen/Arrow - Enemy turned ally.
- Slade Wilson - Ally turned enemy.
- Cyrus Gold - Ally.
- Isabel Rochev - Ally turned enemy.