RIO DE JANEIRO — American Claressa Shields made history Sunday afternoon, becoming the first U.S. boxer to win back-to-back Olympic gold medals, defeating the Netherland’s Nouchka Fontijn in the women’s middleweight (75 kg).

This is gold medal story of survival, escaping from poverty and a difficult childhood, bouncing between 11 homes by the time she was 12, turning all of that pain into a champion boxer.

It is a story of growth and maturity.

After winning the gold at the 2012 Olympic Games in London, Shields did not get the money or fame or endorsements that she expected. She was perceived to be strong, tough and fierce and didn’t have a marketing team behind her. After winning the gold medal, life didn’t get easier. When everybody thought Shields had become rich, there she was, going to a collection agency to pay her mother’s past-due water bill.

But she is older now, more mature and has control of her life.

She split from her longtime coach, Jason Crutchfield, who had coached her when she started boxing at 11 and had been a father figure in her life.

In May, she moved to the U.S. Olympic Training Center in Colorado Springs, Colo, staying in a dorm. The move was to simplify her life, trying to avoid the distractions in her hometown of Flint, Mich.

But along the way, she has also learned responsibility.

“The difference is, now that I’m grown, I make a lot of decisions in my life,” Shields said, earlier this week. “I kind of protect myself. When I was 17, my coach would turn off my phone for me. He would ask me was I OK all the time. He would check on me constantly. He would see me on Twitter at 1 o’clock in the morning and he’d be like, what are you doing? Go to bed.’

“Now, it’s like, I have to tell myself to do those things. Go to bed. Drink right. Eat right. Don’t stay up too late. Don’t stay in the shower for 20 minutes, because it’s like a steam room. Get in there for 5 minutes and get out. I have to keep reminding myself these things. I’m telling myself to focus.”

With this win, Shields becomes the most successful U.S. Olympic boxer in history — the only one to win two gold medals. That should be applauded.

But she is not — not yet, at least — the most accomplished boxer in Olympic history. A pair of Cuban’s have won three golds each: Teoifilo Stevenson dominated the men’s heavyweight from 1976-1994 and then Felix Savon won three in a row from 1992-2000.

Shields is not the most accomplished female boxer in Olympic history, either. Here in Rio, Nicola Adams, who is called the “smiling Yorkshire assassin,” won the flyweight boxing division for Britain for the second straight Olympic Games.

That’s not, in any way, to diminish what Shields has done.

But she still has some work to do, to become the greatest Olympic boxer in history.

But she is only 21, and she certainly has time for that.