John Wick's History
Jardani Jovonovich (Russian: Джордани Йованович, Belarusian: Ярдані Яванавіч) was born in Padhorje, Byelorussian SSR, Soviet Union (Now Belarus) on September 12, 1964. He was orphaned at a young age before being taken in by an old friend of his father, who eventually became John's mentor. At one point, he was recruited by a Ruska Roma organized crime group and trained by its leader, a woman known as "the Director", in New York City. John became associated with many members from the many branches of the Ruska Roma around the world, including Katia, who became his surrogate sister. Under the Director's supervision, John was trained as a hitman and learned skills including martial arts, firearms and other weaponry, tactical driving, infiltration, escapology, and thievery. John later adopted the name "Jonathan Wick," or "John Wick" for short as the anglicized form of his birth name.
It is revealed in the John Wick comic book mini-series that he spent a significant portion of his adolescence in El Sauzel, Mexico and was also depicted that one point in his life, he went on a mission to avenge his childhood hometown and fifty civilians who were destroyed/killed by a gang. He also encountered Charon, an old acquaintance, and saved his life after witnessing some assassins who were holding him at gunpoint opposite to the room he was living in. This would be the catalyst to their friendship as Charon told John he owed him a life debt.
Military Career
John was shown to have a tattoo across his back reading "Fortis Fortuna Adiuvat" ("fortune favors the bold"), which would imply that he was once in the United States Marine Corps, but this has yet to be confirmed. If he was, it was likely he was a member of the Special Operations Command component of the branch, given his extensive knowledge of security surveillance and being able to strategically plan things very well, although this is just speculation.
Career as a Hitman
Years after leaving the Ruska Roma, John became a professional hitman who earned the nickname Baba Yaga ("The Boogeyman" in Russian) for his unparalleled hyper-lethality. He joined the Continental in New York City, a hotel chain catering exclusively to criminals. His reputation for peerless efficiency and reliability earned him considerable respect and fear within the criminal underworld, as well as his persistence to go after those who earn his anger, making him a legendary figure, known to the leaders of virtually all criminal organizations as someone never to be crossed.
John eventually joined a Russian criminal organization known as the Tarasov Mob, becoming one of the main executors of its leader, Viggo Tarasov, who valued and respected John's exceptional abilities, and once saw John kill three men in a bar with a single pencil. During this time, Wick developed relationships with various other criminals working for the High Table, the highest known power in the international criminal underworld, comprised of delegates representing each controlling mafia family. However, John also made a considerable array of enemies - unsurprising, given his profession - including Ms. Perkins, Cassian, and Ernest. In spite of this collection of enemies, John developed valuable friendships with fellow assassins like Sofia Al-Azwar, Caine, and Koji Shimazu, forging a brotherly bond with the latter two. During this time, he even helped Sofia rescue her daughter from the mob, and consequently received a blood oath marker from her, symbolizing her debt to him.
Meeting Helen
John also met a woman named Helen, with whom he fell deeply in love and later married. John decided to leave the uncertain life of an assassin to be with her. When he approached Viggo about retiring, the latter reluctantly agreed to let him leave, but on the condition that he completed an "impossible task": kill every one of Tarasov's rivals in a single night, ensuring his enemies would be completely destroyed before any could mobilize and retaliate.
Completing this task was not considered possible for even John to do alone, and so he sought the help of Italian syndicate leader, Santino D'Antonio, who provided additional manpower and equipment in exchange for John giving him a marker—a decision that would ultimately come back to haunt them both; John figured since he would be free of the criminal underworld, he wouldn't be bound to honor the marker, thus exploiting a rare loophole. Upon completing the task, Wick was released from Viggo's service and the criminal underworld, and allowed to retire to a quiet life as a law-abiding citizen. John and Helen lived peacefully for five years, before Helen's death from cancer, shortly before the events of John Wick.