Venus Williams film to premiere on ESPN Tuesday "I wasn't planning on being that person," said Venus Williams. It was just the right timing, I guess. The winner of 22 Grand Slam titles isn't referring to her place in tennis history as one of the most successful female players ever. Instead, she was talking about a less known time in her career when she stood out not only as an athlete, but as an activist. Williams helped bring about an end to the longstanding practice of paying women less than men at Wimbledon - arguably the most prestigious of the Grand Slam tournaments. Williams' bid for equal pay is chronicled in the ESPN film "Venus Vs.," which airs Tuesday on the sports cable network. The film kicks off a monthlong documentary series called "Nine for IX," which commemorates the 40th anniversary of Title IX. The 1972 amendment to the Higher Education Act of 1965 ensured that women's athletic programs would be funded on an equal footing with their male counterparts. The "Venus Vs." documentary was directed by Ava DuVernay, whose film "Middle of Nowhere" premiered at the 2012 Sundance Film Festival, and landed her the best director prize from the festival. The documentary notes that the fight for equal pay didn't begin with Williams. Billie Jean King, a former No. 1-ranked player and founder of the Women's Tennis Assn., spearheaded a successful drive to force the U.S. Open to pay women equally in 1973. "I'm not trying to be just like her, but I do believe in things, and I'm not afraid to speak up and speak the truth," said Williams during a conference call with journalists last week. I think we have that in common. In 2006, the inequitable pay at Wimbledon prompted Williams to write an op-ed piece for The Times of London, which was published just before the tournament. "We were looking for a place that we could tell our story candidly, and I think The Times story really did that," said Williams. What really made it so grabbing was just how honest it was. The piece led to the involvement of then-Prime Minister Tony Blair and other members of Parliament. By the following year, when Williams won the tournament's women's singles title, she received the same amount in prize money as the male singles winner, Roger Federer. "That's always the goal -- equality across the board, not only in sports, but around the world," said Williams, "You just need to stand up for something that you believe in." Soledad O'Brien joins Al Jazeera America Twitter: @celinecwright