Hreinn Halldórsson (born 3 March 1949) is an Icelandic former track and field athlete who competed in the shot put.

[4] After a ninth-place finish at the 1976 European Athletics Indoor Championships, he entered the 1976 Summer Olympics, where he came 15th in the qualifying round.

This made him the first Icelandic medallist and champion of the competition and he remains he only male to have topped the podium (Vala Flosadóttir won the women's pole vault in 1996).

[5][6] Later that year he threw a personal best of 21.09 m (69 ft 2+1⁄4 in), which ranked him fourth in the world and was an Icelandic national record (he remains the country's second best shot putter after Pétur Guðmundsson).

[7] Halldórsson was unable to translate his indoor win to an outdoor one at the 1978 European Athletics Championships, placing eighth.