Paavo Johannes Nurmi (Finnish pronunciation: [ˈpɑːʋo ˈnurmi] ^ⓘ; 13 June 1897 – 2 October 1973) was a Finnish middle-distance and long-distance runner. He was called the "Flying Finn" because he dominated distance running in the 1920s. Nurmi set 22 official world records at distances between 1,500 metres and 20 kilometres, and won nine gold and three silver medals in his 12 events in the Summer Olympic Games. At his peak, Nurmi was undefeated for 121 races at distances from 800 m upwards. Throughout his 14-year career, he remained unbeaten in cross country events and the 10,000 metres.

Born into a working-class family, Nurmi left school at the age of 12 to provide for his family. In 1912, he was inspired by the Olympic feats of Hannes Kolehmainen and began developing a strict training program. Nurmi started to flourish during his military service, setting Finnish records in athletics en route to his international debut at the 1920 Summer Olympics. After winning a silver medal in the 5,000 m, he won gold in the 10,000 m and the cross country events. In 1923, Nurmi became the first runner to hold simultaneous world records in the mile, the 5,000 m and the 10,000 m races, a feat which has never been repeated. He set new world records for the 1,500 m and the 5,000 m with just an hour between the races, and took gold medals in both distances in less than two hours at the 1924 Summer Olympics. Seemingly unaffected by the Paris heat wave, Nurmi won all his races and returned home with five gold medals, although he was frustrated that Finnish officials had refused to enter him for the 10,000 m.

Struggling with injuries and motivation issues after his exhaustive U.S. tour in 1925, Nurmi found his long-time rivals compatriot Ville Ritola and Sweden's Edvin Wide ever more serious challengers. At the 1928 Summer Olympics, Nurmi recaptured the 10,000 m title but was beaten for the gold in the 5,000 m and the 3,000 m steeplechase. He then turned his attention to longer distances, breaking the world records for events such as the one hour run and the 25-mile marathon. Nurmi intended to end his career with a marathon gold medal, as his idol Kolehmainen had done. In a controversial case that strained Finland–Sweden relations and sparked an inter-IAAF battle, Nurmi was suspended before the 1932 Games by an IAAF council that questioned his amateur status; two days before the opening ceremonies, the council rejected his entries. Although he was never declared a professional, Nurmi's suspension became definite in 1934 and he retired from running.

Nurmi later coached Finnish runners, raised funds for Finland during the Winter War, and worked as a haberdasher, building contractor, and stock trader, becoming one of the richest people in Finland. In 1952, he was the lighter of the Olympic Flame at the Summer Olympics in Helsinki. Nurmi's running speed and elusive personality spawned nicknames such as the "Phantom Finn", while his achievements, training methods and running style influenced future generations of middle- and long-distance runners. Nurmi, who rarely ran without a stopwatch in his hand, has been credited with introducing the "even pace" strategy and analytic approach to running, and for making running a major international sport.

Nurmi was born in Turku, Finland, to carpenter Johan Fredrik Nurmi and his wife Matilda Wilhelmiina Laine. Nurmi's siblings, Siiri, Saara, Martti and Lahja, were born in 1898, 1902, 1905 and 1908, respectively. In 1903, the Nurmi family moved from Raunistula into a 40-square-meter apartment in central Turku, where Paavo Nurmi would live until 1932. The young Nurmi and his friends were inspired by the English long-distance runner Alfred Shrubb. They regularly ran or walked six kilometres (four miles) to swim in Ruissalo, and back, sometimes twice a day. By the age of eleven, Nurmi ran the 1500 metres in 5:02. Nurmi's father Johan died in 1910 and his sister Lahja a year later. The family struggled financially, renting out their kitchen to another family and living in a single room. Nurmi, a talented student, left school to work as an errand boy for a bakery. Although he stopped running actively, he got plenty of exercise pushing heavy carts up the steep slopes in Turku. He later credited these climbs for strengthening his back and leg muscles.

At 15, Nurmi rekindled his interest in athletics after being inspired by the performances of Hannes Kolehmainen, who was said to "have run Finland onto the map of the world" at the 1912 Summer Olympics. He bought his first pair of sneakers a few days later. Nurmi trained primarily by doing cross country running in the summers and cross country skiing in the winters. In 1914, Nurmi joined the sports club Turun Urheiluliitto and won his first race on the 3000 metres. Two years later, he revised his training program to include walking, sprints and calisthenics. He continued to provide for his family through his new job at the Ab. H. Ahlberg & Co workshop in Turku, where he worked until he started his military service at a machine gun company in the Pori Brigade in April 1919. During the Finnish Civil War in 1918, Nurmi remained politically passive and concentrated on his work and his Olympic ambitions. After the war, he decided not to join the newly founded Finnish Workers' Sports Federation, but wrote articles for the federation's chief organ and criticized the discrimination against many of his fellow workers and athletes.

In the army, Nurmi quickly impressed in the athletic competitions: While others marched, Nurmi ran the whole distances with a rifle on his shoulder and a backpack full of sand. Nurmi's stubbornness caused him difficulties with his non-commissioned officers, but he was favoured by the superior officers, despite his refusal to take the military oath even at the threat of a court-martial. As the unit commander Hugo Österman was a known sports aficionado, Nurmi and a few other athletes were given free time to practice. Nurmi improvised new training methods in the army barracks; he ran behind trains, holding on to the rear bumper, to stretch his stride, and used heavy iron-clad army boots to strengthen his legs. Nurmi soon began setting personal bests and got close for the Olympic selection. In March 1920, he was promoted to corporal (alikersantti). On 29 May 1920, he set his first national record in 3,000 m and went on to win the 1,500 m and the 5,000 m at the Olympic trials in July.

Nurmi made his international debut in August at the 1920 Summer Olympics in Antwerp, Belgium. He took his first medal by finishing second to Frenchman Joseph Guillemot in the 5000 m. This would remain the only time that Nurmi lost to a non-Finnish runner in the Olympics. He went on to win gold medals in his other three events: the 10,000 m, sprinting past Guillemot on the final curve and improving his personal best by over a minute, the cross country race, beating Sweden's Eric Backman, and the cross country team event where he helped Heikki Liimatainen and Teodor Koskenniemi defeat the British and Swedish teams. Nurmi's success brought electric lighting and running water for his family in Turku. Nurmi, however, was given a scholarship to study at the Teollisuuskoulu industrial school in Helsinki.