Above all else, Maria Sharapova was a competitor on the tennis court, as intense and as ferocious as anyone who has ever played the sport. And while competitiveness is celebrated in men, and seen as a big plus, women are quite often put down for it. I can relate to that, and I think that was sometimes tough for Sharapova.

But Sharapova, who announced last week that she was saying goodbye to tennis, didn't ever change who she was as a person, or let go of who she was as an athlete, just because other people didn't happen to like her competitive nature. Let me put it this way, you wouldn't have wanted her as your opponent, she wouldn't take her foot off the gas even for a moment.

READ MORE: Maria Sharapova retires from tennis

Throughout her career, Sharapova marched to the beat of her own drum - she wasn't in tennis to win popularity contests, whether with the public or her peers, and perhaps she wasn't always as appreciated as she could have been, but she did what she needed to win, and that worked for her.

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Right to the end of her career, Sharapova still had the same mental toughness that had always defined her. That never left her. That's why the last couple of years must have been so tough for her, as she was trying just as hard as she had always done. Her mind hadn't changed, but her body was saying: 'Naah, it's not going to happen anymore.' That had to be frustrating for her because the effort was there but the results weren't, so I wasn't surprised to hear she had decided to hang it up. I had been expecting this news for a while.

IN PICTURES: Celebrating Maria Sharapova’s champion career

While Sharapova won Wimbledon at 17, I don't think that was her greatest achievement. In my view, that Wimbledon run wasn't as impressive as her two French Open titles in her twenties. In her early years on the tour, as a clay-court player she called herself a "cow on ice" because of the way she was moving and playing on the surface. Back then, her game was much better suited to hard courts and grass than it was to clay. But Sharapova kept at it until clay became her best surface at the end - the French Open was the only major that she won twice.

Those two titles at Roland Garros were an illustration of how Sharapova made the most of what she had, and how she adapted her game. While Sharapova was hitting huge forehands and backhands, she knew that she wasn't the best all-round player so she worked at her game. She improved her drop-shot and her game at the net. Up until her shoulder injuries and surgeries, Sharapova had a great serve. But after her shoulder surgery her serve was never the same again. More than anything else within her game, be it her body or head, her serve let her down the most. And when your serve isn’t there for you, it really bleeds into the rest of your game both physically and emotionally.

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Sharapova will be partly judged by her record against Serena Williams. Unfortunately for Sharapova, you can be the most mentally tough player in the world but sometimes there will be a player you just don't match up that well against, and that was Williams. That match-up against Williams just didn't favor her, particularly as the American certainly served a lot better. Sharapova was good enough against everyone else but Williams always got up for her matches against the Russian. To her credit, Sharapova never relented in those matches, that wasn't in her nature.

I'll remember Sharapova's career for her sheer competitiveness, for her never giving anything less than her absolute best.

Maria Sharapova retires from tennis