| Birth Date: | 24 February 1921 |
| Birth Place: | Braine-l'Alleud, Belgium |
| Death Date: | 6 May 1992 (aged 71) |
| Death Place: | Braine-l'Alleud, Belgium |
| Height: | 173 cm |
| Weight: | 61 kg |
| Sport: | Athletics |
| Event: | 1000-10,000 m |
| Pb: | 1500 m – 3:45.2 (1952) Mile – 4:02.8 (1952) 5000 m – 14:10.8 (1951) 10,000 m – 30:18.8 (1951)[1] |
| Club: | USG |
| Show-Medals: | yes |
Gaston Étienne Ghislaine Reiff (24 February 1921 – 6 May 1992) was a Belgian runner. He competed at the 1948 and 1952 Olympics in the 5000 m event and won it in 1948, defeating Emil Zátopek in the final and becoming the first Belgian track and field athlete to win an Olympic title. He lost to Zátopek at the 1950 European Championships, placing third.
Reiff competed in boxing and football before changing to athletics. Besides his Olympic gold medal he set world records in the 2000 m, 3000 m and 2 miles and won 24 national titles; in 1951 he held Belgian records on distances ranging from 1000 m to 10000 m. A street in Braine-l'Alleud and the town's stadium are named after Reiff in his home town of Braine-l'Alleud.[2]