Karl Hugo Wieslander (11 June 1889 – 24 May 1976) was a Swedish track and field athlete who competed in the long jump, high jump, shot put, discus throw, javelin throw, pentathlon and decathlon. He is best known for his performances at the 1912 Summer Olympics in Stockholm, where he finished second in the decathlon behind Jim Thorpe. Following Thorpe’s disqualification for violating amateur status rules, Wieslander was declared the Olympic champion and was awarded the gold medal, which he refused to accept. Thorpe was reinstated as the 1912 decathlon champion by the International Olympic Committee (IOC) in 1982, and in July 2022 the IOC officially reinstated Thorpe’s gold medal, designating Wieslander as the silver medalist.
Wieslander set the inaugural world record in the pentathlon in Gothenburg in 1911, scoring 5 516 points. At the 1908 London Olympics he competed in the long jump, discus throw, shot put and both the conventional and freestyle javelin events, placing fifth in the freestyle javelin. In addition to his Olympic participation, he won four Swedish national titles: high jump (1907), decathlon (1909) and pentathlon (1910, 1911). His personal bests included a long jump of 6.56 m (1912) and a high jump of 1.80 m (1908).
Beyond athletics, Wieslander passed the state surveying exam in 1913 and worked for the Swedish cartography agency (Rikets allmänna kartverk). He later donated his 1912 Olympic gold medal to the sports museum at the Swedish School of Sport and Health Sciences; the medal was stolen in 1954 and never recovered. Wieslander died in Bromma, Stockholm, at the age of 86.