|Representing the Soviet Union|
|1980 Moscow||200 m freestyle|
|1980 Moscow||4×200 m freestyle|
|1976 Montreal||4×200 m freestyle|
|1980 Moscow||4×100 m medley|
|World Championships (LC)|
|1978 Berlin||4×200 m freestyle|
|1978 Berlin||200 m freestyle|
|1977 Jönköping||4×200 m freestyle|
|1981 Split||200 m freestyle|
|1981 Split||4×100 m freestyle|
|1981 Split||4×200 m freestyle|
|1977 Jönköping||4×100 m freestyle|
Sergey Viktorovich Koplyakov (Russian: Серге́й Викторович Копляков; born 23 January 1959) is a Russian-Belarusian swimmer who won two gold medals competing for the Soviet Union at the 1980 Summer Olympics.
Sergey Kopliakov moved into top ranks of world swimming in 1979, coming behind Vladimir Salnikov, Andrei Krylov and Volodymyr Raskatov, enabling the Soviet Union to fully compete in male freestyle with American champions in the late 1970s. In sports history, Kopliakov will be the swimmer who ended 15 years of American domination in the 200 m freestyle and the first man who bested the time of 1:50 (on 7 April 1979 he achieved 1:49.83 in East Berlin).
Born in Orsha, Belarus' 11th-largest city, Kopliakov debuted in 1974, at the age of 15. He won the 200 m juniors in a people's tournament in 1969. From Minsk he went to Leningrad, one of the pilot centers of the new Soviet swimming and was selected in 1976 for the Montreal Olympic Games, where he won a silver medal in the 4×200 m. His best time in 200 m that year was 1:53.37. In 1977 he was very discreet, only got a fifth place in the 200 m of the European Championships. In 1978, in the West Berlin World Championships, he finished third in the 200 m, behind two Americans with a time of 1:51.33 (new European record). He achieved high recognition in 1978, beating on 7 April the 200 m world record, during the first split of one 4×200 m relay in a GDR/USSR meeting; after that he won the 100 m in 51.46 and the 200 m of the Europe Cup (London) in August and finally the 200 m of the Spartakiad in Moscow in September with 1:50.13, showing himself as one of the most serious opponents for the American swimmers.