Sergei

Sergei was a member of the Russian branch of the Assassins during the late 19th and early 20th century.

Sergei was tasked by the Assassin Order to bring Nikolai Orelov back to Russia, who had severed ties with the Brotherhood years ago. Stating that the Mentor wanted him to return to Russia, as Nikolai had come into contact with the Imperial Sceptre and also been witness and the only survivor of the Tunguska explosion, Sergei then threatened Nikolai's son's safety when Nikolai refused to comply. Nikolai, provoked by Sergei's threat, then prompty killed the Assassin.

Source

 * Assassin's Creed: The Chain