Jarno Karl Keimo Saarinen (11 December 1945 – 20 May 1973) was a Finnish professional Grand Prix motorcycle road racer. In the early 1970s, he was considered one of the most promising and talented motorcycle racers of his era until he was killed during the 1973 Nations Grand Prix in Italy. Saarinen's death led to increased demands for better safety conditions for motorcycle racers competing in the world championships. He remains the only Finn to have won a motorcycle road racing world championship. Saarinen was inducted into the F.I.M. MotoGP Hall of Fame in 2009.
Saarinen's success didn't go unnoticed as Yamaha contracted him to ride their 250cc and 350cc motorcycles for the 1972 season. The Yamaha factory gave him the second 250cc Yamaha TD-3 (YZ635) after Barry Sheene complained about its performance at the third round in Austria. Saarinen rewarded Yamaha's faith in him by winning the 250cc World Championship in a tight season-long battle with Renzo Pasolini and Rod Gould. He finished second in 350cc World Championship, giving defending champion Giacomo Agostini a strong challenge by winning three races, including a victory at the German Grand Prix held at the daunting Nürburgring race track, where Saarinen defeated Agostini for the first time in a head-to-head race. He also scored a double victory at the Czechoslovakian Grand Prix with victories in both the 250cc and 350cc classes. The threat from Saarinen's performance was so strong that the previously dominant MV Agusta factory was forced to produce a new 350cc motorcycle for Agostini. After the world championship season ended, Saarinen traveled to Great Britain where he won the Race of the Year invitational held at Mallory Park.
At the end of the season, Saarinen negotiated with the Benelli factory about the possibility of riding 350cc and 500cc Benellis in the world championships. After a secret test ride at Modena, he rode Benellis to victories over Agostini in the 350cc and 500cc races at the Pesaro street circuit. The Yamaha factory reacted to the possibility of losing their star rider by signing Saarinen to a factory-backed sponsorship to compete on the newly developed YZR500 for the 1973 season. He would also defend his 250cc world championship for the Yamaha factory. The factory sponsorship also meant that he was provided with mechanics for his motorcycles, freeing him to concentrate on racing. With Saarinen signed to a contract, Yamaha was finally ready to challenge MV Agusta's sixteen-year reign in the 500cc class with competitive equipment.