Salwa Eid Naser is a Nigerian-born Bahraini sprinter who specialises in the 400 metres. She was the 2019 World champion with the third fastest time in history of 48.14 seconds, becoming the youngest-ever champion in the event and also the first woman representing an Asian nation to win that event at a World Championships. The mark places her only behind contested results of Marita Koch and Jarmila Kratochvílová. Over the distance, at only 19, Naser was the 2017 World silver medallist. She has also won, as a member of Bahraini mixed-gender 4x400 m relay team, the 2019 World Championships bronze medal.

The 400 metres, or 400-meter dash, is a sprint event in track and field competitions. It has been featured in the athletics programme at the Summer Olympics since 1896 for men and since 1964 for women. On a standard outdoor running track, it is one lap around the track. Runners start in staggered positions and race in separate lanes for the entire course. In many countries, athletes previously competed in the 440-yard dash (402.336 m)—which is a quarter of a mile and was referred to as the "quarter-mile"—instead of the 400 m (437.445 yards), though this distance is now obsolete.