Serena Williams lifted her first Grand Slam trophy at the young age of 17, winning the 1999 US Open. Along with that triumph came a handsome check of US $750,000 - her highest payday by far at the time.
Sister Venus soon followed suit and won the Wimbledon Championships the next year, cashing in about £200,000 for the win.
The prize money for those two titles does fade in comparison to their current collective net worth of US $335 million (as estimated by Forbes). However, the historic wins on two of the sport's biggest stages were the start of their journey to stardom.
Venus and Serena Williams, who made their debuts at the age of 14 and 13 respectively, owned the big stage right from the start. An Olympic singles gold (2000 Sydney) for Venus and the duo's first doubles title at a Grand Slam - at Wimbledon - brought them huge recognition, after which sponsorships began to pour in.
Venus, who signed a record eight-figure deal with Reebok in 1995, renewed her contract in 2000. She signed a $40 million deal with the same brand that covered the next five years.
Serena, meanwhile, moved from Puma to Nike for her own five-year, $40 million deal.
The duo's earnings soared as they continued to do well at the big events. The sisters also launched their own business ventures eventually.
EleVen, Venus Williams's activewear clothing brand, was launched in 2007. The 40-year-old has created several memorable designs over the years and continues to run the enterprise successfully.
Serena didn't jump into business straight away, but her on-court earnings through the 2010s sustained her success. She earned a mammoth $12.4 million in 2013, a record for single season earnings that still holds.
As their stature grew with their unmatched on-court success, high-profile sponsorship deals from the likes of Aston Martin, Ralph Lauren and Pepsi followed quite naturally.
As per Forbes, Serena Williams alone had 20 corporate partnerships in 2021. She makes up for $240 million of the total $335 million net worth of the combined duo. However, Serena continues to credit her elder sister for opening the doors for black athletes and women with her trailblazing journey to the top of the game.
"I think you get to really see the ecosystem of my family" - Venus Williams on King Richard
Richard Williams, Serena and Venus' father, introduced his daughters to the sport that they would go on to become an indispensable part of. But in addition, he also brokered the duo's first sponsorship deals.
Richard's story forms the basis of the Will Smith-starrer King Richard, which released on 19 November. Venus Williams spoke to ABC News shortly after the release, saying that the film really showed the "ecosystem" of her family in the early years.
Venus also spoke about the difficulties her father faced during the early years, before adding that eventually people began to see him as someone who's all "for his family."
"I think you get to really see the ecosystem of my family," Venus Williams said. "It's not perfect, but all that matters is that you are going in the same direction together and building each other up. That's what we did and that's what we do."
"People didn't understand him but I think that it didn't take long for people to realize that this is a guy who's for his family, for his daughters, ride or die, no matter what," she added.