The answer to this question is mainly because Herb Elliot set different world records in running during his era. He was born Herbert James Elliot on February 25, 1938 in Subiaco, Western Australia and he was motivated by the sporting culture at his school, Aquinas College. He set a world record in the mile run in 1958 when he finished the track in just a matter of 3 minutes and 54.5 seconds.
Later that month, he set another world record in 1500 meters in just 3.36 seconds. It was in the 1960 Rome Olympics did he get a gold medal and broke his own world record with a time of 3 minutes and 35.6 seconds. He retired shortly afterwards, got married and had a child.