In 1967, Kathrine Switzer made history by being the first "official" female runner to run the Boston Marathon.

This week, at 70 years old, she crossed the marathon's finish line wearing her original bib number.

Since her historic run (she registered using her initials), Switzer has become a hero for women in sports. Her race in 1967 revealed a massive sexism problem in athletics: There was no official rule barring women from entering the race; still, it was frowned upon.

Switzer showed up to the 1967 race wearing lipstick and earrings, fully and unapologetically advertising her gender. She was told to remove her lipstick (which she refused) and was jeered at by male runners.

In her memoir, Switzer recalls race director Jock Semple grabbing her arm and attempting to remove her from the race.

She writes:

"Instinctively I jerked my head around quickly and looked square into the most vicious face I'd ever seen. A big man, a huge man, with bared teeth was set to pounce, and before I could react he grabbed my shoulder and flung me back, screaming, 'Get the hell out of my race and give me those numbers!'" 

Switzer finished the race but was later disqualified. She went on to run 39 marathons and become an advocate for women's rights in athletics. She created the Avon International Running Circuit of women's-only races in 27 countries, as well as 261 Fearless, a nationwide, nonprofit running club for women.

Dropping out of the race back in 1967 was simply out of the question for Switzer, as she writes on her website:

"I knew if I did that no one would believe women could run distances and deserved to be in the Boston Marathon; they would just think that I was a clown and that women were barging into events where they had no ability. I was serious about my running and I could not let fear stop me."

On Monday, Switzer crossed the finish line of the 2017 Boston Marathon, greeted by a chorus of cheers from spectators and a medal from a race official.

The Marathon will officially retire Kathrine's bib number, 261, in her honor.

H/t: CNN