Environmental advocate Erin Brockovich became world-famous when Julia Roberts won a Best Actress Oscar playing her in the 2000 film bearing her name.

Directed by Steven Soderbergh, it told the story of her David-versus-Goliath victory leading a multi-million-dollar lawsuit against a utility company that poisoned a California town's drinking water.

Now, there is a drama series inspired by her, Rebel, streaming on Disney+ from tomorrow.

It stars Golden Globe winner Katey Sagal as Annie "Rebel" Bello, a blue-collar legal advocate who has no law degree, but will do anything for the causes and people she fights for.

But the real Brockovich might be even more colourful than her fictional avatar, according to Sagal.

This was unmistakable the first time she met Sagal and Krista Vernoff, who wrote and produced the series and is also the showrunner for medical drama Grey's Anatomy (2005 to present).

Says Sagal, the 67-year-old star of crime drama Sons Of Anarchy (2008 to 2014): "I got it just sitting and hanging out with her because the passion and the fire comes across even over lunch."

The character Rebel also captures Brockovich's unique gifts as a legal and consumer advocate, which often stem from the fact that she is not a lawyer.

"What I love so much about Rebel is that she can cross a few lines and go outside the box. It's not that she does anything illegal, but she pushes a bit further and can gather knowledge from everywhere," Sagal says during an online press panel.

"Her primary purpose is to fight for the right thing. I think sometimes legal mumbo jumbo can make that confusing when it's actually a very straight line in terms of what's right."

Brockovich, 60, is an executive producer on the show, and she and Sagal worked together to develop the character, who also has a messy personal life and a husband (John Corbett) who is divorcing her.

But it was not about Sagal asking Brockovich which details of the show and character were true to life.

"That didn't have to happen because Katey just gets it," says Brockovich. "She just oozes it. It's her energy and her presence. She's a bada**."

Vernoff, 47, says the writers found an invaluable resource in Brockovich, now a media personality and a consultant for law firms. "Erin visited our writers' room, and we listened and we absorbed and we tried to put it into the script," she says.

The series is not just a rehash of the 2000 film, which was nominated for the Oscar for Best Picture. Instead, it draws from more recent occurrences in Brockovich's life. "It's a different character. I'm older, wiser, more evolved," Brockovich says.

The character also reflects what she admits is her sometimes volatile nature, and the fact that she does not always react in a cool and calm way.

"I am still just as frustrated at being underestimated or put into a box, which results in me trying to jump out of that box however I can," she says.

But that unpredictability is what makes her a thrilling muse, says Vernoff. "If Erin edited herself more effectively, we'd have a way less exciting, dramatic and comedic TV show."

So, rather than a dry procedural legal drama, the series is "very sexy and it's about family, friendship and all of the human interactions - with a legal element".

"Whenever I'm on set and a director asks me, 'Is it supposed to be funny or dramatic? Is she supposed to be angry or does she really love him?', my answer is always 'both'," Vernoff adds.

"There's no binary. There's no either/or, there's no funny or dramatic. Erin is all of those things at once in her work and in her humanity, and Katey brings it to life so beautifully."

• Rebel is available on Disney+ from tomorrow.