Ivan Joseph Martin Osiier (December 16, 1888 – December 23, 1965), was a Danish Olympic medalist, and world champion, fencer who fenced foil, épée, and saber.

[4][5][6] His parents were Martin Moses Meyer Osiier (1861–1933) and Hanne Henriette Ruben (1865–1922).

[1][4][12] He is one of only four athletes who have competed in the Olympics over a span of 40 years, along with sailors Magnus Konow, Paul Elvstrøm, Durward Knowles and showjumper Ian Millar.

[13] Apart from competitions, Osiier worked for the Denmark Fencing Federation as their leader.

[1][4] Osiier was inducted into the International Jewish Sports Hall of Fame in 1986.