<Li> Michael Rowe portrays Floyd Lawton / Deadshot, a mercenary who killed Andy Diggle under H.I.V.E.'s orders . Lawton is also a member of the Suicide Squad, although he is killed on a mission in season three . In season four it is revealed that Lawton did not kill Andy, but was used by H.I.V.E. to fake Andy's death . </Li> <Li> Colin Salmon portrays Walter Steele, Moira's husband, Oliver's step - father, and Felicity's former employer . He was president of Queen Consolidated until he disappeared in episode 9, but was found alive in episode 21 . He and Moira separate at the end of season one, and he returns in season two to help her run for mayor . It is revealed that Moira had confided in Walter about Thea's true paternity at some point after they marry . He is currently the chief financial officer of Starling National Bank . </Li> <Li> Jamey Sheridan portrays Robert Queen, Moira's late husband, Oliver's father, and Thea's legal father . Despite his marriage to Moira, Robert was not a faithful husband, having many illicit affairs outside of his marriage including with his company's intern, Isabel Rochev . Robert is secretly aware that Thea is Malcolm Merlyn's biological daughter, but accepted her and also acted as a surrogate father to Malcolm's son, Tommy . As a young man, Robert gained his wealth through corrupted means including killing a local councilman, Henry Goodwin; he gradually become remorseful of his greed, leading him to join Malcolm's secret society, Tempest, to improve Starling City's condition in hope of making amends . He and Oliver were both lost at sea when Malcolm sabotaged the Queen's Gambit . Robert sacrifices his life by killing himself, increasing Oliver's chances of survival and returning home to Starling City to right Robert's wrongs . </Li> <Ul> <Li> Cynthia Addai - Robinson portrays Amanda Waller, leader of A.R.G.U.S. and commander of the Suicide Squad . In season two, Waller often forces John Diggle to work for her on missions other A.R.G.U.S. agents are unwilling to perform . She tries to have Starling City destroyed during Slade Wilson's attack to contain the Mirakuru soldiers, only to be stopped by John and Lyla . She has used the codename "Mockingbird". She is killed after the Shadowspire soldiers infiltrate A.R.G.U.S. in season four . In the season three flashbacks, she rescues Oliver from Lian Yu after witnessing his progressive skills in combat, and forces him to work for her and, in the process, furthers his trainings two years prior to his return to Starling City . </Li> <Li> Kevin Alejandro portrays Sebastian Blood / Brother Blood, a savvy politician who is working with Slade Wilson, a friend of Oliver Queen and romantic interest of Laurel Lance . He is a city alderman who is running for mayor to create his vision of Starling City . He leads a double life as a criminal, wearing a skull mask based on the nightmares he had of his late - father, called "Brother Blood". Seemingly benign, over the course of season two Sebastian is gradually revealed to be narcissistic and directly responsible for the murders of his parents . When Oliver and Laurel are close to discovering his secret, he misdirects them by having Laurel kill a decoy in the skull mask . Laurel uncovers his secret and Oliver tries to reason with Sebastian . Sebastian is betrayed by Slade, causing him to give the Mirakuru cure to Oliver, for which he is killed by Isabel Rochev . </Li> <Li> Summer Glau portrays Isabel Rochev, a senior executive at Stellmoor International who acquires half of Queen Consolidated in the second - season premiere . She later secures full control of the company in a hostile takeover . It is revealed she was Oliver's father's mistress during her internship and had been working with Slade to get revenge . Like Oliver, Isabel was also trained by Slade in martial arts, but she was later injected with the same Mirakuru drug that was given to Slade . In the season two finale Isabel is killed by Nyssa al Ghul . The character shares her name with the DC Comics villain "The Queen", who, in the comics, became CEO of Queen Industries following the death of founder Robert Queen . </Li> <Li> Grant Gustin portrays Barry Allen / Flash, a young crime scene investigator from the Central City Police Department . Oliver first meets Barry when the latter arrives to personally investigate a superhuman - related crime in Starling City . Barry discovers that Oliver is his vigilante idol, the Arrow, saves Oliver's life and helps him to begin uncovering the Mirakuru plot orchestrated by Slade Wilson . Ultimately, both Barry and Oliver become good friends and they occasionally offer each other advice and support . Barry later gains the power of super-speed, and is inspired by Oliver's example to become a hero known as the "Flash". He occasionally joins Oliver on missions and remains a trusted friend and ally . Gustin stars as the character on The Flash . </Li> <Li> Katrina Law portrays Nyssa al Ghul, the daughter of Raʾs al Ghul . Nyssa is said to have encountered a dying Sara on Lian Yu after Oliver and Slade's fight on the Amazo, and brought Sara to the League where they became lovers, though her father never approved of their relationship . In season two, when Sara leaves the League, Nyssa works to force her return, threatening her family, but ultimately accepts her departure and later helps Oliver fight Slade's army when Sara decides to return to the League . In season three, when Sara is murdered, Nyssa goes on a vengeance quest to kill Malcolm, correctly assuming he is her killer though he claims otherwise . She befriends Sara's sister, Laurel, but her animosity with Oliver intensifies because he is unwilling to let her execute Malcolm . Nyssa feels betrayed when Raʾs declares Oliver his successor and releases Malcolm, and she leaves Nanda Parbat for Starling City and begins training Laurel . Nyssa is later captured by Oliver, Maseo Yamashiro and a team of assassins to bring her back to Nanda Parbat by force, for stealing the Alpha / Omega virus from the League . Instead of having Oliver kill Nyssa for her betrayal, Raʾs decides that the two should marry, to her evident dismay . However, Nyssa aligns herself with Oliver and his team to save Starling City, defying her father . She later returns to the League under Malcolm's leadership and bows to him despite making it clear that she intends to kill him one day . In season four Nyssa begs Laurel not to use the Lazarus Pit to bring Sara back to life, knowing Sara will return different . When Laurel does so regardlessly, Nyssa retaliates by using a potion Raʾs Al Ghul left to destroy the Pit . Nyssa later escapes and tries to manipulate Oliver into killing Malcolm by leveraging him with the cure to Thea's condition, though this results in war between her and Malcolm . Eventually Nyssa succeeds when Oliver defeats Malcolm without killing him and Nyssa disbands the League to spite Malcolm and regain Team Arrow's trust . She later returns to attend Laurel's funeral . </Li> <Li> Caity Lotz portrays Sara Lance / Canary / White Canary, Laurel's sister with whom Oliver had an affair . Sara, along with Laurel and their mother Dinah, is based on the DC Comics superheroine Black Canary . She was believed to have drowned with the sinking Queen's Gambit, but she resurfaces in season two as another vigilante, the "Canary", who is connected to the League of Assassins . She was originally portrayed by Jacqueline MacInnes Wood in the pilot . According to Kreisberg, she is "the beginning of the Black Canary story". She eventually wins her freedom from the League and returns to Starling City, to become part of Oliver's team in addition to working as a bartender at his nightclub . She breaks with Oliver over a dispute concerning Roy, and rejoins the League in order win their backing against Slade Wilson's army . She returns to Starling City on a mission for the League, but is killed by a mysterious archer . It is revealed that Thea killed Sara while drugged and controlled by Malcolm, as part of a plot to force Oliver into combat with Raʾs al Ghul . Lotz dubs Cassidy's lines when Laurel impersonates Sara as the Canary, and later appears as a hallucination of Laurel's . In season four, Laurel, Thea, and Malcolm resurrect Sara using the Lazarus Pit, but she returns mentally fractured until Oliver brings in his old friend, John Constantine, to help restore her soul . However, Sara's behavior remains volatile and she suffers an insatiable bloodlust, which prompts her to seek solitude away from home . </Li> <Li> Dylan Neal portrays Dr. Anthony Ivo during flashbacks in season two . He is the first character in the series who tells Oliver, Slade and Shado about the "Mirakuru"; he later murders Shado . After one of his hands has been cut off by Slade, he is killed by Oliver on Lian Yu . </Li> <Li> David Nykl portrays Anatoli Knyazev, based on the character KGBeast . Anatoli was kidnapped by Dr. Ivo and is brought to Lian Yu where he meets Oliver Queen and becomes a friend and is instrumental in Slade's defeat on the island . Sometime between the flashbacks and the present, Anatoli makes Oliver a Bratva captain and continues to assist him in the present . </Li> <Li> Danielle Panabaker portrays Caitlin Snow / Killer Frost, a bioengineering expert from S.T.A.R. Labs and a metahuman with cryokinetic abilities . Caitlin helps Felicity in recreating the Mirakuru antidote, and occasionally helps Team Arrow on missions . Panabaker stars as the character on The Flash . </Li> <Li> Graham Shiels portrays Cyrus Gold, an acolye of Brother Blood who is the first to survive injection with Mirakuru in the present day . Oliver defeats him in the episode "Three Ghosts". </Li> <Li> Bex Taylor - Klaus portrays Cindy a.k.a. "Sin", a wayward youth who Sara takes under her wing in Starling City after Cindy's father is killed on Lian Yu . Cindy later befriends Roy Harper and Thea Queen . </Li> <Li> Carlos Valdes portrays Cisco Ramon / Vibe, a mechanical engineering genius at S.T.A.R. Labs with known metahuman abilities to detect anomalies within reality and sonic manipulation . Cisco helps upgrade the arsenals of Oliver, Laurel, and Sara, aids Ray with his Atom suit, and designs a new safe house for Oliver . Valdes stars as the character on The Flash . </Li> </Ul>

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