Kathrine Switzer, the first woman to officially enter and run the Boston Marathon once said, "If you are losing faith in human nature, go out and watch a marathon."

Marathons are an incredible mix of pain and determination, anguish and triumph, courage and fear. And whether you run in one or cheer on others from the sidelines, it's impossible to walk away uninspired.

Octogenarians Kay and Joe O'Regan (pictured above) recently celebrated their 80th birthdays and 57th wedding anniversary by running the Cork City Marathon in Ireland. As a testament to their bond, the pair crossed the finish line hand-in-hand, earning them the hashtag #relationshipgoals on Twitter and beyond and inspiring generations of running couples and singletons around the world.

Every runner who completes a marathon has a story to tell. But these are the stories that have inspired runners all over the globe to take on the challenge of the marathon, one step at a time.

1960 Rome Olympics, Abebe Bikila

Abebe Bikila Abebe Bikila ran and won the 1960 Rome Olympic Marathon without shoes. (Photo: Central Press/Getty Images)

Abebe Bikila was added to the 1960 Ethiopian Olympics Marathon team at the last minute to replace another runner who had become ill. When Bikila tried to get fitted for shoes from that year's Olympic sponsor, Adidas, he found that they didn't have any left that fit him comfortably. So he decided to run the race in the same footwear that he ran in at home: none.

When he won the race in a record time of 2 hours, 15 minutes and 16 seconds, he became the first Sub-Saharan African to win an Olympic gold medal in any event. And he was the first and only person to win the Olympic marathon by running barefoot. As if that weren't enough, Bikila won the marathon again at the 1964 Tokyo Olympics (this time wearing shoes), becoming the first person in history to win the Olympic marathon twice.

1966 Boston Marathon, Bobbi Gibb

Bobbi Gibb Bobbi Gibb crossed the finish line of the 1966 Boston Marathon wearing a bathing suit and her brother's Bermuda shorts. (Photo: Gatorade/YouTube)

It may sound hard to believe, but in 1966, just 50 years ago, it was unheard of for a women to run a marathon. Doctors advised women not to run at all as the standard medical belief at the time was that a woman's "fragile" reproductive organs might fall out with such vigorous exercise. So when 24-year-old Bobbi Gibb applied to register for that year's Boston Marathon, she was not surprised to receive a letter from race organizers denying her request because "women are not physiologically able to run marathons."

But Gibb knew what she could do and she knew that the only way to prove to the world that women could run the marathon distance was to just do it. Wearing a black bathing suit, her brother's Bermuda shorts, and a hoodie to cover her hair and face, Gibb hid out in the bushes near the start of the legendary race, joining a pack of runners as they passed by. When Gibb crossed the finish line in 3 hours and 21 minutes, she became the first woman to complete the Boston Marathon. "I think it was a pivotal event in changing the perception of women," she said in an interview with Women's Running magazine. Because if women could run a marathon even though all of the experts said they couldn't, then what else could they do?

1967 Boston Marathon, Kathrine Switzer

Kathrine Switzer In this now legendary photo series, you can see race organizer Jock Semple attempt to rip the race numbers off Kathrine Switzer during the marathon. (Photo: BBC News/YouTube)

Fast-forward one year from Bobbi Gibb's amazing run in the Boston Marathon; it's 1967, and women are still banned from the marathon. But Kathrine Switzer got into the race by using her pen name, K.V. Switzer, on her application. She became the first woman to run the Boston Marathon wearing official race numbers.

Like Gibb, Switzer knew that history was on the line with her run, so she didn't stop moving for the entire 4 hours and 20 minutes of her race, even when race organizer Jock Semple accosted her mid-run in an attempt to rip the race numbers off her shirt.

1984 Olympic Marathon, Los Angeles, Joan Benoit Samuelson

Joan Benoit Samuelson Joan Benoit Samuelson's epic win at the 1984 Los Angeles Olympics was broadcast around the world. (Photo: Bennett Running/YouTube)

In 1972, women were finally admitted to the Boston Marathon, but it wasn't until the 1984 Olympics in Los Angeles that women were allowed to compete in the 26.2-mile footrace at the Olympic level. Prior to that race, marathon organizers had continued to insist that it was unhealthy for women to run — and that there weren't enough women interested in running marathons to justify an Olympic slot.

The televised 1984 Women's Olympic Marathon brought women's running into the living room of girls and women around the world. And when American Joan Benoit (now Joan Benoit Samuelson) crossed the finish line exuberantly in an amazing time of 2 hours, 24 minutes, and 52 seconds, she laid to rest any remaining doubts about the abilities of women runners.

2011 Toronto Waterfront Marathon, Fauja Singh

Fauja Singh Fauja Singh became the first centenarian to finish a marathon when he crossed the finish line of the Toronto Waterfront Marathon in 2011. (Photo: Getty Images)

Running is often considered a young person's sport. But no one ever said that to British Sikh Fauja Singh, who didn't even start running until the age of 89. Singh took up running after the deaths of his wife and son as a way to recover his zest for life. Before long, he was running 10K races, and in 2011, at the Toronto Waterfront Marathon, Singh became the first centenarian to finish a marathon-distance race. His time of 8 hours 11 minutes and 6 seconds is still the record for the 100-plus age group today.

Singh retired from marathons at the age of 102, though he continues to participate in shorter distances like 5Ks and 10Ks around the world.

2013 New York City Marathon, Tatyana McFadden

Tatyana McFadden Tatyana McFadden crosses the finish line at the New York City Marathon. (Photo: Elsa/Getty Images)

Life got off to a rocky start for Tatyana McFadden. She spent her first six years in an orphanage in St. Petersburg, Russia. Born with spina bifida that left her paralyzed below the waist, McFadden got around by crawling on her hands as the orphanage did not have the funds to buy her a wheelchair. But all of that changed when she was adopted by American Deborah McFadden and brought to the U.S. to live.

McFadden took to sports almost instantly — wheelchair basketball, sled hockey, swimming — and any other sport she could find to play. That athletic prowess helped her become an Olympic parathlete in both Nordic skiing and track and field where she has won three gold, five silver and three bronze medals. As if that weren't inspirational enough, in 2013, McFadden became the first athlete ever — abled or physically challenged — to win four major world marathons in a single year after claiming victory in the women’s wheelchair division of the 2013 London, Boston, Chicago and New York City marathons.

2016 Boston Marathon, Patrick Downes

Patrick Downes An emotional embrace between Patrick Downes and his wife after he crossed the line in Boston. (Photo: Maddie Meyer/Getty Images)

In 2013, the running community was devastated when bombs went off at the finish line of that year's Boston Marathon, killing three spectators and injuring 264 others. Patrick Downes, who had been cheering at the finish line with his wife, lost his left leg in the explosions. His wife lost both of hers.

Not to be deterred, Downes returned to Boston in 2016, this time not as a spectator — but as a runner. Fitted with a prosthesis, Downes completed the Boston Marathon in 5 hours, 56 minutes and 46 seconds, becoming the first Boston bombing amputee to complete the race entirely on foot.

2016 Olympic Marathon Trials, Los Angeles, Amy Cragg

Amy Cragg and Shalane Flannagan Shalane Flanagan collapsed into Amy Cragg's arms at the finish line of the Olympic Marathon Trials. (Photo: Joshua Blanchard/Getty Images)

As running fans around the world sat down to watch the Women's Olympic Marathon Trials in February 2016, the question on everyone's mind wasn't who would make the team to represent the U.S. in Rio, but rather, who else would make the team along with race-favorite and defending trials champion Shalane Flanagan. Prior to that race, Flanagan had so many American records and championship titles to her name that her spot on the team seemed like a lock. And Flanagan made it clear that she not only hoped to make the Olympic Marathon team, but she also planned to help her teammate and training partner, Amy Cragg, punch her ticket to Rio as well.

But as anyone who has ever completed a marathon can tell you, things rarely go as planned during those 26.2 miles. In the final miles of the race, the unusually warm and sunny weather started to unhinge Flanagan. And though she and Cragg had a considerable lead over the rest of the field, it was clear to everyone that she was losing ground. Cragg, who had finished fourth at the 2012 Olympic Marathon trials and thus missed out on her chance to go to the London Games, had every reason to leave Flanagan behind. But that's not what she did.

“Our dream has been to get on the team together. Not just one of us, both of us on the team,” said Cragg at the post-race press conference.

In what can only be defined as the ultimate act of loyalty, Cragg stayed by Flanagan's side, talking to her, handing her water, and keeping her teammate in the race. With just one mile to go, as a third competitor — Desi Linden — closed ranks on the pair, Cragg gave Flanagan some final words of encouragement before she took off for the finish. Cragg finished the race in 2 hours, 28 minutes, and 20 seconds just ahead of Linden's 2 hours, 28 minutes, and 54 seconds. When Flanagan crossed the line in 2 hours, 29 minutes, and 19 seconds — earning her third place and a spot on the Olympic team — she collapsed into Cragg's arms.

“Sweet baby Jesus, I am so thankful for her,” Flanagan said of Cragg’s support through the final miles during what she called "the hardest marathon I've ever run."

Now, don't you feel inspired to go for a run?