AP Photo/Alberto Pezzali

She is the greatest of all time.

Serena Williams, who has won a record 23 Grand Slam singles titles, is leaving tennis after 27 years.

In a first-person article, she announced her decision.

Serena Williams @serenawilliams

A must read. https://t.co/NSWDGHzsXK

I don't like the wordretirement. It doesn't feel modern to me. I want to be careful about how I use that word because it means something very specific and important to a community. I think the best word to describe my work is evolution. I'm here to let you know that I'm moving away from tennis and towards other things that are important to me.

She won 14 women's doubles titles with her sister and two mixed doubles titles with Max Mirnyi.

She was the reigning champion for all four Grand Slams twice.

Williams started as a pro at the age of fourteen. She defeated Lindsay Davenport and Monica Seles over the course of a few years. She won her first Grand Slam in 1999 at the US Open.

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She became the top ranked women's tennis player in 2002 after winning Wimbledon. Over the course of two years, she won 12 singles titles. She won five of the six Grand Slam titles she played in.

Williams' career has been characterized by her ability to return to her elite form after taking time away to rehabilitate from serious injury. She became one of the game's greats when she came back.

She had surgery on her thigh injury late in the year. She was out for a long time. She won the 2005 Australian Open less than a year after coming back from a serious injury.

Williams took a break from the game in order to take care of her mental health. She won the Australian Open one year after reaching the quarterfinals of all four Grand Slams.

She had a foot injury in 2010 that kept her out for the rest of the year and she said she was depressed during her time away.

She went on to win 126-11 in matches and 273-33 in sets over the course of two years. When she won 11 titles, she went 78-5 and 160-15.

Williams came back to tennis after giving birth.

She had a caesarean-section in September of last year. She was hospitalized for six weeks after giving birth to her daughter.

She made the Wimbledon and U.S. Open finals over the course of four years after returning to competitive tennis. The US Open and Australian Open semifinals were made by Williams.

Williams wants to focus on growing her family and venture capital firm in the future. She says there is pain when you leave tennis.

There is no joy in this topic for me. I know it's not normal to say that, but I feel a lot of pain. It's the most difficult thing I've ever imagined. I don't like it I don't like that I have to make a decision. I want it to be easy for me, but it isn't. I'm ready for what's next but I don't want it to end.

Her professional tenure has been legendary and her resume speaks for itself.

Williams has been a competitor for nearly three decades.