Born on Sur'Kesh, Tann's application to the Andromeda Initiative lists his previous work experience as "Senior Consultant, Advanced Matrix-Based Accounting" with hobbies in model ship building and "travel...someday".
Mass Effect: Andromeda: Nexus Uprising
Jarun was originally appointed Deputy Assistant for Revenue Management within the Andromeda Initiative, but after the seven leaders above him perished when the Nexus collided with the Scourge in 2818, including Initiative founder Jien Garson, he was thrust into the role of Director of the Initiative. During this dire stage, hydroponics was damaged, there were no habitable planets available, and supplies were stretched to a crisis point.
Lacking Garson's charisma, Jarun had an uneasy relationship with the other Initiative leaders and was frequently derided as a less than ideal placeholder. His dealings with Nakmor Kesh are especially tense due to Jarun's prejudice against the krogan. As the situation became more dire, Tann began entertaining the idea of putting people back into cryostasis and installing rationing policies. After the Nexus' scout teams failed to find habitable worlds, Tann decided to forcefully send people back into cryostasis to conserve their resources. Dissent turned to open rebellion against the Nexus leadership, causing the event known as the "Nexus uprising".
Relations between Head of Nexus security, Sloane Kelly, and Tann quickly deteriorated during the uprising. Sloane was vehemently against using the krogan against the mutineers and went to negotiate with the rebellion's leader— Calix Corvannis. While she was away, the Director went behind her back to make a deal with Clan Nakmor in order to decisively put down the mutiny. Calix Corvannis was killed in the ensuing violence with the krogan and upon learning of the Director's intervention, Sloane switched sides and joined the rebellion. To deal with the rebels and their supply problems in one fell swoop Tann gives them an ultimatum: exile to the hostile planets or cryostasis. The rebels and Sloane chose exile. When Clan Nakmor approached Tann about their promised reward of political representation on the Nexus, the salarian revealed he was only just learning about their deal with William Spender and reneges on it, claiming Spender wasn't authorized to make such a deal and that the human will be "reprimanded" for the error. Tann narrowly escaped the wrath of Nakmor Morda due to Kesh standing between him and her clan leader. Kesh convinced Clan Nakmor to follow the outlaws into exile and noted Kesh's presence on the Nexus would ensure the krogan would have an ally in the Nexus despite their departure from the station.
Mass Effect: Andromeda
Director Tann has official oversight of Initiative operations and strategy, and effective supervision of Pathfinder teams. However, many still consider Tann inept at handling the chains of command and he lacks the charisma to enforce his authority. Thus, Tann and a council of prominent Nexus leaders have to reach a consensus to provide any form of effective leadership for the Andromeda Initiative; a practice not easily realized as the Nexus leadership is often hampered by squabbles and debates on political issues.
Although Pathfinder Ryder lacks Alec Ryder's experience, Tann recognized Pathfinder Ryder as the Nexus' best chance at finding habitable worlds and overcoming the obstacles of the Kett and the Scourge. Thus, Tann used his authority to provide Ryder the Tempest. Tann hoped Ryder's success in making a world viable for an outpost would result in waking more colonists up from cryostasis and gathering more resources to support the Nexus. Should Ryder succeed, Tann's endorsement of them would enhance his political reputation, and should they fail, Tann rationalized that he could aggrandize himself through the endorsement of another Pathfinder.
After Ryder succeeded in activating the Remnant vault to render Eos habitable, allowing the Initiative to establish an outpost, Tann compliments the Pathfinder's achievements. When Kandros and Kesh comment on whether Ryder establish a military or scientific outpost, Tann overrules them, reminding that they can't take back the decision. He subsequently approves Ryder's request to investigate a lead on the vault network. This leads to the Initiative making first contact with the angara.