Almost 20 years since they turned pro, the Williams sisters still serve as an inspiration to each other, whether that involves handling personal tragedies or rebounding from illnesses or injuries.
For instance, 17-time Grand Slam winner Serena overcame a pulmonary embolism in 2011, the same year seven-time Grand Slam champ Venus was diagnosed with Sjögren's Syndrome.
"She's the ultimate inspiration," Serena said. "To go through what she's gone through is such a great story. If it was me, I probably would have hung up my racquets and maybe played some doubles. She has so much courage to show up week in and week out and play. That's what I call courage."
Changes in Venus' lifestyle, specifically her diet as she battles the autoimmune disease, have rubbed off on Serena.
"We live together," Serena said. "My mom started, and then I started. I felt like I couldn't bring bad things in the house. And I love to cook, so I learned how to cook, well raw, and I learned how to cook vegan and stuff like that. So it was a great experience for us all.
"It's a great way to live. It's so healthy. Forget tennis and everything. It's just about living a healthy lifestyle and being the best person you can on the inside and healing your body from the inside out."
Serena has witnessed firsthand the ups and downs of Venus' valiant comeback the past few years.
"It's just amazing because I know what she goes through more than anyone else, and sometimes she's doing great and sometimes it's difficult," Serena said. "She might lose matches that she would normally win 10 times out of 10, but to accept that and keep going is really amazing."
Venus had similar sentiments about how Serena has affected her.
"I learned a lot from Serena in the early '90s, '98 and '99, because she had a lot of heart, and I felt like I needed to be more like that," Venus said. "So she was a great role model for me.
"Serena is an inspiration not just for me but I think for every woman on the WTA and for so many more men, women and children who aren't playing tennis. So just around the world, she's an inspiration."
And the Williamses don't just inspire each other, but other players like Caroline Wozniacki.
"I think they are great role models," the Danish former World No.1 said. "They do a lot of charity work. I think they are great for the game, because they stand up for the players. They are on the council. They do a lot for the WTA, not just as players, but also how they represent the tour, which I think is great."
The Williams sisters are next scheduled to be in action in three weeks in Madrid, where Serena is the two-time defending champion.