Max Austin is a former assassin for the KGB.
When we first meet him, he is retired from that organization. That is to say, the KGB does not exist anymore since the government for which it functioned had ceased to exist. Seeing a chance to get out from their control, Austin used the confusion to move to Paris and create a new life and new identity for himself. He bought into a jazz club and now makes a fair living.
He augments that income by using his old training and taking an occasional "job" for a very limited group of people, by which I mean he does the odd hit when the intended target falls within Austin's personal set of criteria warranting elimination.
Austin's preferred weapon for use in eliminating his targets is the garrote, his preferred version of which was two strands of piano wire secured at each end by wooden dowels called a la loupe. The two strands were created by using one long piece of wire, coiled to create the double strands such that if the victim was able to get his hand between the wire and his neck, "they'd only succeed in making the other coil tighter". I mention to to show how disciplined and conscientious Austin is in his job. Of course, for backup he routinely has a SIG Sauer P224, a subcompact, in a shoulder holster.
Now, when we meet him for the first time, he is Mikhail Asimov, nicknamed Max, who hails from Minsk in what is now the country of Belarus but when he was born, it was one of the states in the Soviet Union. His was an odd upbringing. He and his younger sister, Arina, had a mother who, at least to Max, was "cold and distant, uninvolved in his childhood, often judgmental and harsh". It was his father, Andrei, who was the parent both spent the most time with and this is an important fact because all through their formulative years, Andrei was considered one of the best agents the KGB had. "Such was the life of the children of one of Moscow’s most celebrated spies. While the other kids were playing stickball, Max and Arina had been learning tradecraft from their father."
"At sixteen, Max had left Minsk to attend military school in Moscow. From there he’d disappeared into the Russian Army, then the KGB. During the infrequent visits home, all his time had been spent with his father." Then the USSR dissolved, Max left for Paris and his new job (or jobs) and time passed. Until his distant mother caught cancer and had only a short time to live and Max heads back to Minsk and all sorts of troubles ensue.
And in the smoke of all that trouble will step Kate Shaw, described a force of nature all her own, working as a major player in the CIA and someone who will offer Max a new life when his previous one explodes, literally. Working for the Agency while they help him find out who attacked his family. And use the killing skills he had developed with the KGB to work for its former biggest rival.
Oh, he is given a new identity. The Agency has suggested Max Sienkiewicz. He said no and picked for himself the name Max Austin.