|Full name||Gennadi Borisovich Sosonko
|Born|| May 18, 1943
|Peak rating||2595 (January 1981)|
Gennadi (Gennady, Genna) Borisovich Sosonko (Russian: Геннадий Борисович Сосонко; born 18 May 1943, Troitsk, Russia) is a Dutch chess Grandmaster (GM).
At the beginning of his career, in 1958, he won in the Leningrad juniors championship.
Sosonko moved from the Soviet Union to the Netherlands via Israel in 1972. This was a highly publicised defection, which led to the USSR Chess Federation pressuring FIDE to declare him an "unperson".
He won the Dutch Championship in 1973 and 1978 (jointly). His tournament record includes 1st at Wijk aan Zee 1977, 1st at Nijmegen 1978, 3rd at Amsterdam 1980, 1st at Wijk aan Zee 1981, 3rd at Tilburg 1982 and 4th at Haninge 1988. He also drew a match with Jan Timman (+1 =0 −1) in 1984.
Sosonko played eleven times for Dutch team at the Chess Olympiads in 1974-84, and 1988-96. He won two individual medals: gold at Haifa 1976, bronze at Nice 1974, and two medals for team: silver at Haifa 1976, and bronze at Thessaloniki 1988.
FIDE, the World Chess Federation, awarded Sosonko the International Master (IM) title in 1974, the GM title in 1976 and the FIDE Senior Trainer title in 2004.
Sosonko has authored four non-technical chess books centering heavily on his chess life in the Soviet Union and his relationships with and memories of both leading Soviet players and lesser-known characters in chess history.