Caitlyn Marie Jenner was born William Bruce Jenner on October 28, 1949, in Mount Kisco, New York, to Esther Ruth (nee McGuire) and William Hugh Jenner. Her father was an arborist. She has two sisters, Lisa and Pam. Her younger brother, Burt, was killed in a car accident in Canton, Connecticut on November 30, 1976, shortly after Jenner's success at the Olympic Games.

Jenner was the American champion in the men's decathlon event in 1974, and was featured on the cover of Track & Field News magazine's August 1974 issue. While on tour in 1975, Jenner won the French national championship, and a gold medal at the 1975 Pan American Games, earning the tournament record with 8,045 points. This was followed by new world records of 8,524 points at the U.S.A./U.S.S.R./Poland triangular meet in Eugene, Oregon on August 9-10, 1975, breaking Avilov's record, and 8,538 points at the 1976 Olympic trials, also in Eugene. The record in Eugene was a hybrid score because a timing system failure and wind aided marks. Still, Jenner was proud of "A nice little workout, huh?"  "We got what we wanted. We scared the hell out of everybody in the world only a month away from the Games."  Of the 13 decathlons Jenner competed in between 1973 and 1976, the only loss was at the 1975 AAU National Championships, when a "no height" in the pole vault marred the score.  At the 1976 Olympic Games in Montreal, Jenner achieved five personal bests on the first day of the men's decathlon - a "home run" - despite being in second place behind Guido Kratschmer of West Germany. Jenner was confident: "The second day has all my good events. If everything works out all right, we should be ahead after it's all over." Following a rainstorm on the second day, Jenner watched teammate Fred Dixon get injured in the 110 meter hurdles, so took a cautious approach to the hurdles and discus, then had personal bests in the pole vault, when Jenner took the lead, and javelin. By that point, victory was virtually assured, but it remained to be seen by how much Jenner would improve the record. In the final event--the 1500 meters, which was seen live on national television--Jenner looked content to finish the long competition. Jenner sprinted the last lap, making up a 50-meter deficit and nearly catching the event favorite, Soviet Leonid Litvinenko, who was already well out of contention for the gold medal, but whose personal best had been eight seconds better than Jenner's personal best before the race. Jenner set a new personal best time and won the gold medal with a world-record score of 8,618 points.  Olympic world record performance:

How many medals did they win?