One of the things you will notice about Venus Vs. is that Serena Williams, Venus’ younger (now more accomplished) sister has no presence to speak of. The documentary – the first in ESPN’s new “Nine for IX” series – chronicles Venus’ compelling mission for equal pay at Wimbledon, where purses for tennis’ most storied grand slam tournament paid its women’s winner less than its men’s. When asked why Serena was such a non-presence in a film documenting perhaps her sister’s crowning achievement – since, surely Serena had some insight – director Ava DuVernay was pointed.

“It was Venus’ cause,” said DuVernay (who recently won the Best Director prize at the Sundance Film Festival for Middle of Nowhere). “This was Venus’ passion. She put this cause on her back. I think it’s lazy to put [Venus and Serena] together all of the time.”

The two sisters are less than a year removed from the release of Venus and Serena. The two sisters also recently appeared on the cover of The New York Times magazine. We use “Venus and Serena” like we are referring to one person – “Venus&Serena.” Sometimes we forget that these are very individual women whom we’ve taken to linking at all times.

Or, as DuVernay bluntly put it: “It becomes ridiculous to always feel like these people are thinking and behaving in similar ways.”

This documentary was a clear indication of that, as it becomes evident that Venus – and Venus alone – should be mentioned along with Billie Jean King and Martina Navratilova when it comes the most socially impactful women’s tennis players.

Venus Vs. first takes some time to recall Venus’ very immediate cultural disruption of the WTA tour (players speak of knowing that Venus was nearby because you could hear the beads on her braids, and the film’s most emotional moment comes from footage of a teary-eyed, teenage Venus pleading with a line judge who had just penalized her a point because a bead flew off during play). But it briskly moves on to the subject of gender inequity.

“Venus was an outsider who became the ultimate insider,” said DuVernay, herself a Compton native. “She was able to revolutionize a key tenet in her sport. She had this kind of allergy to injustice.”

There was a meeting in 2005 between Venus, the WTA brass, Wimbledon officials and 10 other top women’s pros. Venus’ voice was the most impactful. Then there was her op-ed in the London Times in 2006 where she called the on-going lack of equal pay a “shame.”

DuVernay said, for Venus, who signed a $40 million contract with Reebok in 2000, it wasn’t really about the money.

“Venus was so flushed, so paid, she didn’t have to [campaign for equal pay]. It was the principle,” she said. “The money was nominal. It was the notion that you would withhold from her something that she’s earned.”

It’s almost startling that one of the most famous athletes in the world could lead a charge of such social significance in her sport and that the story go largely uncovered here in America. DuVernay said this was a huge story in the UK last decade, but it failed to resonate stateside. This makes for a very revealing documentary. We learn new things.

Toward the end of Venus Vs., it’s said that this was a story about Venus versus chauvinism, Venus versus the establishment and Venus versus herself.

“This woman was an activist,” said DuVernay. “And this cause ignited that in her.”