Anton Gregorovich is a minor character in the Alex Rider's spin-off Russian Roulette. He was a chemical and biological researcher, The husband of Eva Gregorovich and the father of Yassen Gregorovich. Anton and Eva's deaths sent Yasha down a dark path into becoming skilled assassin "Yassen" Gregorovich.
Anton Gregorovich was born in Moscow, Russia. He was a researcher of chemical properties and a biologist; engaged in research at the University of Moscow. Anton was hired to create a deadlier version of anthrax that would eliminate lives instead of saving them. They were forced to create transferable quantities of the virus for the Russian military; under the facade of producing pesticide for farmers. His wife later gave birth to a son, Yasha.
An accident at the factory caused the outbreak of the virus, infecting their son. Yasha's parents were able to reach their son in time and inject him with an antidote which they had created, thus saving his life. However Anton was shot and killed in by enemy soldiers in the process. This event sent Yasha down a dark path, eventually changing his name to "Yassen" and becoming an enemy agents of SCORPIA as Cossack.