Since the Williams sisters first burst into tennis in the 1990s, their legacy has been tied to one another. They will play doubles in perhaps the final tournament of their careers.The Williams sisters. They are the yin to the other’s yang. Starkly different in disposition but tied together by history and sisterly bond.Serena Williams, of course, has been the unquestionable North Star of this U.S. Open. After announcing plans to “evolve” away from tennis once she strikes her last ball here, she is the darling of the tournament and indeed the sports world — lauded and feted and dripping in diamonds and light for her swan song.Venus Williams, at 42 the trailblazer and older of the two, has willingly settled into the backdrop, as has become customary since Serena grabbed the mantle of most famous and accomplished sister.But with Venus’s years piling up and her ranking stuck in the 1500s, this may well be her finale, too.Venus took to the court for her first-round match this week with the statuesque, Zen-like calmness that has been her trademark for years. Through an error-prone loss played in front of a muted, half-full Arthur Ashe Stadium, Venus’s bearing never broke.At virtually every moment of her defeat, 6-1, 7-6 (7-5), to Alison Van Uytvanck of Belgium, she was the picture of chin-up, shoulders-back regality.We tend to take the greats for granted, especially when greatness comes in two. It’s easy to forget that among the sisters, Venus burst onto the world stage first. As an unseeded 17-year-old, she marched to the finals here in 1997.“It’s been such an amazingly long career that people lose track of what she was back then and at her peak,” said Lindsay Davenport, who lost to Venus in the championship match of the 2000 U.S. Open (Venus won again in 2001). “She was so powerful, serving at 120 miles per hour, all over you with every shot, running down everything.”Those days are gone. What has never diminished is the unyielding interdependence Venus and Serena share.Lindsay Davenport recalled facing Venus Williams in 2000. “She was so powerful, serving at 120 miles per hour, all over you with every shot, running down everything.”Vincent Laforet/The New York TimesEarly in the week, Serena, 40, described Venus as “my rock” and spoke of how important it was to have Venus be part of this week’s celebration. For the first time since 2018, and most likely the last time ever, the two will play in a Grand Slam doubles tournament.With a mischievousness glimmer, Venus told reporters she had no choice in the matter. It was Serena’s idea. “She’s the boss so I do whatever she tells me to do,” she said.Since the mid-1990s, they have been playing professional tennis on an unrelenting tour that offers little time for rest and plenty of time to feel isolated and alone.Serena Williams’s Farewell to TennisThe U.S. Open could be the tennis star’s last professional tournament after a long career of breaking boundaries and obliterating expectations.Decades of Greatness: Over 27 years, Serena Williams dominated generation after generation of opponents and changed the way women’s tennis is played, winning 23 Grand Slam singles titles and cementing her reputation as the queen of comebacks.Is She the GOAT?: Proclaiming Williams the greatest women’s tennis player of all time is not a straightforward debate, our columnist writes.An Enduring Influence: From former and current players’ memories of a young Williams to the new fans she drew to tennis, Williams has left a lasting impression.Her Fashion: Since she turned professional in 1995, Williams has used her clothes as a statement of self and a weapon of change.It’s a grind for top competitors like the Williams sisters, who for years made it their business to reach the last stages of almost every event they played. Add race to the mix — the fact that, as Black women, Venus and Serena were always symbols of something much more than just themselves — and the pressure deepens.That they had one another all this time was more than a blessing, it may have helped keep both of their careers going well past the typical due dates.They had one another, and we watched them both.The sisters faced off 16 times in major tournaments, almost always in late rounds. Venus won five of those matches. How many Grand Slams would Serena have won if Venus were not there to fend her off? And what about the other way around?There were Venus’s walloping wins the first three times they played on tour. And the nervous way they played as the rivalry approached full stride.Serena’s balky performances led to awkward post-match hugs. “No, no, you, little sis, take the next one,” Venus seemed to reply. “I just can’t play the way I want against you.”They had a habit of playing so poorly against one another that some in tennis fandom became convinced that their father, Richard, had fixed their matches. When Venus pulled out with an injury just before their semifinal match at Indian Wells in 2001, the conspiracy theory reached a peak.Venus sat in the stands as Serena battled Kim Clijsters in the final of that tournament, the predominantly white crowd angrily booing both of the sisters and, according to Richard Williams, shouting a racial slur. They were 20 and 19 at the time.From 2002 to 2003, Serena began taking over as the sister destined for ultimate greatness. In that period, they faced off in the finals of four consecutive Grand Slams. Serena won them all.Did this cause sibling jealousy? Not for these two.Having just lost to her sister at the 2002 French Open, Venus was so proud and delighted for Serena that she stepped off the podium, retrieved a camera and joined the press photographers taking photos of the newly crowned champion.Having just lost to Serena Williams at the 2002 French Open, Venus joined the group of photographers to get a shot of the newly crowned champion.Photo by Phil Cole/Getty ImagesTheir on-court rivalry became one-sided over the last dozen years, decidedly swinging in Serena’s favor, but on and on they went, always together, always close, Venus ever the careful big sister with the broad shoulders to lean on.Would either have reached the highest of heights if the other’s example had not provided a constant push to improve? Remember, Venus won seven Grand Slam singles titles and a stunning 14 playing doubles alongside Serena.Then consider all that the sisters have gone through together. The murder of their half sister Yetunde Price in 2003. Venus’s 2011 diagnosis with Sjogren’s syndrome, a fatigue-causing autoimmune disorder. Serena’s pulmonary embolism that year and, later, near-fatal post-pregnancy complications.Would they still be playing if they were solo acts and not siblings?One of the most beautiful things about their careers is the way we’ve witnessed both of them mature and learn from both success and embarrassing failure.Venus spoke to this after her first-round loss when asked about her role in helping Serena conclude that the time was right to leave tennis.“We’re a huge influence on each other,” she said, “and I’m a huge influence on her.”As she continued, Venus noted how she had tried to step away and let her sister’s retirement emerge naturally with Serena, her husband, Alexis Ohanian, and their young daughter, Olympia, taking the lead.“This decision needs to be all hers and her family’s,” Venus said. “The newest part of the family.”Since the 1990s, when they first emerged on the scene, the sisters have been synonymous — tied together in the public mind and their daily reality, a firm knot that never loosened.Time alters everything, though. New family members are central to the equation.Long after this tournament is over, Serena’s story will continue to be there for all to see. Her journey as a venture capitalist or a media mogul is one we will know about. If she has another child, we’ll know that, too: They’ll probably land on the cover of Vogue.Serena will remain in the spotlight. And whenever she needs her sisterly rock, Venus will be there, self-contained and confident, all majestic presence and blistering serve, loyal as can be. More