Yassen Gregorovich was a recurring villain in the series, appearing from the first novel to the fourth. He was formerly a Russian-born contract killer, trained by and apparently working for the clandestine terrorist organization SCORPIA. A superb assassin, Yassen was considered one of the world's best.
For all his skills, Yassen is obviously best known for his assassinations; throughout the series, his reputation seems to be one of a man who makes no mistakes, and is considered an active threat by MI6. It is suggested that his training was grounded in ninjutsu, including, as is demonstrated on a single occasion, basic psychological warfare. He was also supposedly an expert with conventional weaponry and terrorist technique, though both are demonstrated only once throughout the series before his death, in the fourth book. Yassen made another appearance (in a scene set in the past) in the seventh book of the series, Snakehead. He was also revealed to be fluent in 7 languages and was learning Japanese at the time of his apparent death.
Yassen was at least partially instructed by Alex Rider's late father, John Rider, who appeared to be working as an unspecified instructor (though certainly in some form of combat, considering that he was a weapons and martial arts expert) for SCORPIA on the Italian island of Malagosto. However, he was secretly working for MI6 under deep cover.
Yassen is in debt to John Rider; during a joint assignment in the Amazon, Rider saved his student's life by killing a black widow on Yassen's throat; something which Yassen never forgot. Though Alex does not initially realize the reason, Yassen exhibits some care for the boy, on more than one occasion saving (or sparing) his life. At the time of his death (which was caused by a bullet from Damian Cray's gun), Yassen actually tells Alex he loved both John Rider and Alex.
Having trained in a special assassin school in Italy, he killed his first man when he was 19 in the Amazon Jungle. Yassen Gregorovich became a professional and reliable contract killer and is employed by SCORPIA. They sent him on numerous jobs throughout the world. He was apparently killed by Damian Cray in the book Eagle Strike.
Considering Yassen's reputation and position, it is probable that his assassinations are numerous. Throughout the entire series however, only four of Yassen's assassinations are revealed.
Born in Russia, Yassen's father was killed by an accident of a biochemical warfare project that was hushed up by the Russian Government. His mother died 6 months after due to illness. After his parents death, Yassen (who was at the time 14) made his way to Moscow in search of SCORPIA. While in Moscow, Yassen ran errands for the local mafia. Eventually, Yassen Gregorovich found and started to work for SCORPIA.
Yassen Gregorovich is described as attractive, having blond hair, pale blue eyes, pale skin, distinctly chiseled lips, and "almost feminine eyelashes". He also has a long, distinctive scar along his neck caused by John Rider when he saved him from a black widow spider by shooting it off his neck, leaving a mark where the bullet grazed his skin. Yassen's relaxed and graceful poise is often compared to that of a dancer.
From http://en.wikipedia.org/wiki/List_of_Alex_Rider_characters
Yassen Gregorovich
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