Mary Keitany is only 31 years old, so this story is still being written (she turns 32 later this week). So far in her career, she has set a world record in the half marathon (seen above). She ran 1:05:50 on February 18, 2011, and it was the first time a woman broke 1:06 on a non-aided course.
Later in 2011, she ran 2:19:19 and won the London Marathon. This was the tenth fastest time ever run by a woman. In 2012, she was even better. Mary won London again in 2:18:37, which is currently her marathon PR. That is also the fifth fastest time ever run by a woman (behind only Paula Radcliffe and Liliya Shobukhova).
Mary has never won an Olympic medal – she came in 4th in London – but she should have one more shot in Rio. Nevertheless, her blazing speed in the half marathon and her ownership of two of the ten fastest marathons of all-time make her one of the greatest ever.