Alexander Khasinau was a key member in "The Man"'s operations and was allied with the Russian Mafia. Like many others, he was a follower of Rambaldi.
Khasinau was first identified by Sloane shortly after the attack on SD-6. He and other member of The Alliance believed that if they captured Khasinau, they'd find "The Man" and the people who are responsible for the attack. During the investigation though, Edward Poole found out that one of Sloane's friends, Jean Briault, was accepting a wealthy sum of money from Khasinau and was working with him behind their backs. Sloane was forced to kill Briault, despite the fact it was really Poole himself who was working with Khasinau (The Prophecy).
Not much later, K-Directorate sent a hitman nicknamed Snowman to assassinate Khasinau and all of his associates. The assassin killed a man named Igor Valenko, but before the Snowman could find Khasinau, he was killed by Sydney Bristow (Q&A).
Khasinau finally met Sydney face-to-face after she and Vaughn destroyed a Mueller device. Sydney was captured by Khasinau and after conversing with him, who she presumed to be "The Man", was shocked to discover that really his leader was Irina Derevko, Sydney's mother (Almost Thirty Years).
After the meeting with Sydney, Khasinau retreated to a laboratory where he was surgically experimenting with people infected with the water from the Mueller Device. Just as he was about to cut open Vaughn, Sydney came in and was knocked out in a short fight, but escaped with Vaughn while Khasinau was getting help.
Khasinau was later sent to Barcelona to acquire "The Bible", a compilation of all the plans and assets for "The Man"'s organization. However, someone ambushed the meeting when several CIA agents arrived and Khasinau was forced to retreat, although he got The Bible in the confusion. After chasing Khasinau, Sydney fought him in a warehouse just in time for her mother to show up. She pointed the gun at her and fired off a shot...hitting Khasinau instead. Shortly afterwards, he fell backwards and died (The Enemy Walks In).
Why Irina killed Khasinau is unconfirmed, but it was probably because of his numerous failures or the fact that Khasinau was no longer useful to her.