Almost from the moment Venus and Serena Williams appeared on the Grand Slam scene in the late 1990s, they've been winning titles and transcending tennis, becoming red-carpet celebrities as much as sports stars.
Every so often, like all elite athletes, they've heard questions about whether their best days were behind them, whether health problems or off-court distractions were taking their toll. And each time, it seemed, one or the other - or sometimes, amazingly, both - would promptly reach a major final, as if to say, "Hey, don't count us out yet."
Now that each is past her 30th birthday, and big victories are less frequent than ever, those questions are bound to get more persistent, especially after this week. The 2012 French Open has been the worst Grand Slam tournament in Williams family history, the first of the 43 that both entered at which neither reached the third round.
Venus lost 6-2, 6-3 in the second round Wednesday at Roland Garros, barely providing any resistance against Agnieszka Radwanska of Poland, who might be seeded No. 3 but never has been past the quarterfinals at a major tournament. Afterward, Venus spoke about the difficulties of adjusting to living with Sjogren's syndrome, an autoimmune disease that can cause fatigue and joint pain and leaves her listless some days.
Asked whether the thought crossed her mind she might have played her last French Open match, she didn't hesitate for a moment.
"No, not at all," replied Venus, who turns 32 in June. "This is just the beginning for me. This is a process that I have to learn a lot from, working with myself, with my doctors, everything. Like, this is the beginning for me again. I have to be positive. I can't walk out on the court and say, `Oh, my God, this is it.' That's not the way I see it."
Serena, meanwhile, lost 4-6, 7-6 (5), 6-3 in the first round Tuesday to Virginie Razzano of France, a woman who is ranked 111th and never has made it beyond the fourth round at a major tournament. Making it more surprising: Serena was two points from victory nine times but couldn't close the deal. It's the only time in 47 career Grand Slam appearances that the younger Williams lost her opening match.
"There's those days someone comes out and they have nothing to lose, so they go for it. ... It's bad luck. She's a great player. I think if she could have gotten through that match, it would have been, this tournament, a lot different for her," Venus said about her sister. "Thankfully she has, like, 20-something majors to keep her warm at night."
That's true: Counting singles, women's doubles and mixed doubles, the 30-year-old Serena actually owns 25 Grand Slam trophies. Her 13 in singles represent by far the highest total among active women and the sixth most in history. Venus stands second among women on tour now, with seven, the last in 2008. They've teamed up to win 12 in doubles.
They've always been each other's fiercest rival and best friend, ever since they emerged as teenagers from Compton, Calif., coached by a father who taught himself tennis by watching instructional videos. They were siblings who competed with each other for top billing in their own home and the entire globe - and with 120 mph serves and punishing groundstrokes, they ushered in a new brand of power-based play.
All along, they've dabbled in other interests such as fashion (both have worked on clothing lines), interior decorating (Venus' pursuit) and acting (Serena's side project).
"Serena could have been the greatest player ever. Ever," 12-time Grand Slam singles champion and women's sports pioneer Billie Jean King said in a recent interview. "She is the best athlete we've ever had in the game. She and her sister Venus were brought up to do many, various things. So they do go in and out, there's no question. But ... when Serena gets focused, watch out."
Both have been No. 1 in the WTA rankings, but Serena is now No. 5, and Venus is No. 53.
They have played each other in eight Grand Slam finals (Serena leads 6-2), including four in a row from 2002-03, but none since Wimbledon in 2009. Serena's title at the All England Club the next year was the last at a Grand Slam tournament for either Williams; a few days later, she cut her feet on glass at a restaurant, leading to a series of complications, including blood clots on her lung.
Her latest issue was a bad back, although she refused to blame that for her loss to Razzano.
"I've just got to ... figure out what I did wrong and not do it again," Serena said. "You know, learn from it."
There is a new generation of players moving up, and the Williams sisters certainly are at least partly responsible for helping spur the growth of tennis.
Its global reach is such that the top 10 women in this week's rankings represent 10 countries. The past four Grand Slam tournaments were won by first-time major champions - Li Na of China, Petra Kvitova of the Czech Republic, Sam Stosur of Australia and Victoria Azarenka of Belarus - the longest such stretch of debut titles in the Open era, which began in 1968.
Venus and Serena Williams made women's tennis matter more than it had in years, prompting a move from Saturday afternoon to prime time for the U.S. Open title match in 2001, when a pair of sisters met in a Grand Slam singles final for the first time since it happened at Wimbledon all the way back in 1884.
The first all-Williams major final 11 years ago drew higher TV ratings than a college football game the same night between two Top 25 college football teams, Notre Dame and Nebraska.
"I definitely grew up watching them. I've idolized both of them forever. I mean, they were the first players I watched on TV and said, `I want to be there, one day, playing the tournaments that they're playing,"' said Melanie Oudin, a 20-year-old from Marietta, Ga., who reached the 2009 U.S. Open quarterfinals.
"I just can't see them - especially Serena - retiring. Serena's been the best of the best for so long," Oudin continued. "Even when she's out for a while, she comes back, and she can still play amazing tennis and beat everyone."
The world will be watching when Wimbledon begins next month to find out if that's still the case.