Ari Tasarov was the leader of the Russian criminal organization Gogol, an organization seeking to rival and topple Division, as well as serving as the shadow arm of Sergei Semak. Nikita was close to assassinating him, but refrained upon seeing Ari with his son. He is former KGB. He was born on June 30, 1966 in Moscow, Russia
Ari is called in by Mr. Harcourt, the handler of one of his agents who was trying to get close to U.S. Senator Jack Kerrigan, to inform him about how Nikita killed his partner. Ari decides to use Nikita to assassinate Kerrigan, injecting a Division-made poison Gogul reverse-engineered, to liquify her stomach within 12 hours and promises the antidote if she completes the job. However, Nikita outsmarted him, got the antidote from another source and ruin Kerrigan's career. Ari later met with Nikita, offering for them to work together to take down Division, revealing his knowledge of the black boxes.
Gogol goes after Emil Voss and the dirty bomb he developed. During a shootout between Gogol and Division at an airport, Ari intercepted Nikita as she was carrying the bomb away. Before he departed, he reminds Nikita that his offer still stands. But as he drives away, he finds that the suitcase that the bomb was hidden in was switched with a regular one.
Nikita comes to Ari to ask for his help in getting to Kasim Tariq, the al-Qaeda leader whom Gogul has a partnership with. Ari agrees but warns her about getting a third strike with Gogol. After Niktia hit a convoy full of heroin, Kasim goes to St. Petersburg to confront Ari as to who the "Knights of Shi'ra" are. Ari simply bluffs his way through, before Nikita doublecrosses him again, before capturing Kasim.
In "Falling Ash", Ari meets with Owen Elliot, a former Division Guardian, collaborating to find the remaining black boxes. However, Owen warns Ari that if he moves against Nikita, he will kill him. (Falling Ash)
Ari later is summoned by Semak, to investigate the assassination of Anton Kochenko, Zetrov's public liaison, before shooting the man who objected. Ari is also revealed to have collaborated with Kelly, Nikita's old Division partner. In exchange for breaking her out of a Turkish prison in order to draw Nikita out, she'd acquire the black box she has in her possession. While Nikita is trying to get her former partner out of the country, Kelly phones Ari to inform him of a Division agent Nikita strangely wants to spare. Once she gives a description of the agent, Ari realizes that it is the same woman who posed as a photographer at the time of Kochenko's death, Alexandra Udinov. He ordered Kelly to change orders to capture Alex. However, Nikita killed both Kelly and Ari's strike team. Ari later reveals Alex's survival to Semak, who insists that she be killed.
Eventually, Owen tracks down a Guardian, Patrick Miller, only to discover he's gone. Ari threatens to renegotiate the terms of their agreement if he doesn't get results. On advice from Nikita, Owen used Gogol resources to pinpoint any black market developers of the Regimen drug the Guardians are dependent on. Ari, however, convinced Semak to keep the black box instead of destroying it. He captures Owen as soon as he leaves Zetrov HQ, catching him calling someone but the call history had been deleted. Worse yet, Nikita and Miller were arrested by the police for starting a firefight at the Regimen lab and the black box became confiscated. Ari intercepted the police convoy and took the box, ordering his men to finish off Nikita. As he drove away, Michael swooped in an saved both Nikita and Owen.
Ari brought the box back to the Udinov mansion. At the same time, Nikita and Alex began infiltrating the place. Ari became suspicious of certain happenings around the estate and his instincts proved right. Once Katya Udinov confirmed that Alex was in the mansion, Ari captures her before she could rescue her mother. Ari and Semak then question Alex about Percy, having believed that Division captured and brainwashed her instead of killing her. Alex states that Nikita rescued her and Ari believes her.
In "Doublecross", Ari is present when Alex returns to her childhood home with a camera crew, which was a cover to extract her mother. When Alex and Sean Pierce discover that Katya is missing, they confront Ari, who denies any knowledge and suspects that Semak no longer trusts him. He confides in the two that he plans on framing a foreign intelligence agency for Semak's deaths with a deep cover agent.
In "Arising" Ari kills Semak in attempt to take control of Zetrov, intending to frame MI6 agents for the act. He also informs MI6 that Cassandra is a double agent working for the Russians after she betrayed him.
In "With Fire" it was revealed that he has a son, Stefan Tasarov. In "The Life We've Chosen " Nikita agrees to make a trade deal with Amanda ,Alex for Ari, which ends in the results of Ari's death by Amanda.