Gennadi Sosonko is a Soviet-born Dutch Grandmaster of chess. He was born on May 18, 1943 in Troitsk. His father was a Polish Jew and mother was Russian. Sosonko moved to the Netherlands in 1972 before receiving Dutch citizenship two years later in 1974. He is a self-trained player, having not learned chess from any master or academy.
In 1967, Sosonko tied for 1st-2nd place in the URS-ch semifinal, and finished at 4th place in 1970 and 1971. He won the Dutch Chess Championship in 1973 and 1978. In international competitions, he won in Wijk aan Zee in 1974, and at New York 1977. He has also represented The Netherlands in eight Chess Olympiads. Despite never becoming a World Chess Champion, Sosonko was a respected figure and was the European champion in 1972.
Aside from being a professional chess player, Sosonko has also contributed to the chess world through publications. He is a regular contributor to Dutch, German, and Russian-language chess publications. He has also written books about chess, many of which contain profiles of his fellow Soviet grandmasters. He is also noted for his psychological insights into the character of chess players.
Sosonko is a member of the Association of Chess Professionals, which looks after the interests of professional chess players, and was a second for Viktor Korchnoi in the 1977 World Chess Championship Candidate's Match. He was awarded the title of International Master in 1974 and Grandmaster in 1976.