If you want to know what it looks like to be a champion, turn your gaze upon Venus and Serena Williams.

Riddled at times with pain, doubt and fatigue through their often excruciating daily regimen, they know what it takes to be a champion.

In order to understand how two sisters from Compton, Calif., became champions, you have to know a little bit about the man who created them.

The new documentary "Venus and Serena," in theaters May 10, offers a glimpse into the work ethic and the mindset their father instilled in them.

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Richard Williams borrowed used balls from country clubs to coach his young daughters in a sport he never played, in a park infamous for gang activity.

They served and volleyed for as long as six hours a day, and their dad even had them throw racquets hundreds of times to build their serving arm strength. He didn't believe he had the next Michael Jordan; he had the next two Michael Jordan's.

"He raised them with a great deal of love, and he also always gave them a sense of freedom," Michelle Major, who directed the documentary, told ABC News. "He's fiercely protective of them."

He also taught them to be protective of each other - yet another lesson the sisters, just 15 months apart, have mastered.

It's a delicate dance, where they remain each other's biggest rivals, and yet the closest of confidants. They are both Jehovah's Witnesses and both unmarried.

"I feel like I haven't accomplished anything in my career," Serena Williams said. "Maybe that sounds ridiculous, but I feel like I have to do so much more."

Even before Venus Williams was born, their father wrote a 78-page manifesto plotting their trajectory to the top of the tennis world.

"My parents told me I'd be No. 1 in the world," Venus Williams said. "I was brainwashed."

The sisters not only share the same house in Florida, but some of the same hobbies, including karaoke.

"I know they're not twins, but in a way they are," author Gay Talese said. "Their whole life experience has been within the shadow of the other person. There's very little that's happened to any one of them that the other's not been privy to, maybe even witness to."

It's a story of triumph over adversity for a family that mastered the game with a scoring system that always begins with love.

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