No-one was allowed to leave the room until everyone in there changed women's tennis forever.

The knock-on effects of that meeting at the Gloucester Hotel in London 50 years ago, which led to the formation of the Women's Tennis Association (WTA), are everywhere to see today.

In the past decade, only four women have ranked in the top 50 of the Forbes list of the highest-paid athletes. All of them were tennis players.

It is a far cry from where the women were on 21 June 1973, as, led by Billie Jean King, they gathered just before Wimbledon to unite groups of players from rival tours into a single organisation that eventually became the first truly global women's professional sports tour.

"It was a pivotal moment in women's tennis," another of the main protagonists, Rosie Casals - King's doubles partner and fellow member of the 'Original Nine' who formed a breakaway tour in 1970 - told BBC Sport.

But it is one, she feels, that today's generation may not fully appreciate at times.

"We show them the movies and the videos and Billie Jean up there fighting. But they really need to understand it - not just look at it, but grasp that they have had the greatest ride in the world," the American nine-time Grand Slam women's doubles champion said.

"There is no other women's sport to be so successful and entitled the way these women have been.

"It's not just showing up to play tennis and collecting the cheque. They don't even collect the cheque, that cheque goes to their agents, I don't think they've ever put their hands on a cheque.

"I want to see them give more back to the sport and help the sponsors and promoters when they are needed to show up for something.

"I know things are easier, and it's the different times in a different game. It's just like your parents trying to tell you about the Depression. What do you know? They're sitting in probably the best place ever."

'Most of the time you're talking to their agent'

The creation of the WTA did not just happen during the course of those few hours in the conference room.

Casals said she and the others had spent the previous year talking to the players on the rival tour - those like Britain's Virginia Wade and Australian Margaret Court - to persuade them of the merits of joining forces, using the evidence from their breakaway Virginia Slims circuit to illustrate it would be a worthwhile move.

The 'Original Nine' had taken a risk in 1970 by forming their own women's circuit that resulted in them being banned from Grand Slams tournaments, signing a symbolic $1 contract that then paid off as they started to earn good money and play in big arenas.

That success was born from the close relationship the players had with sponsors and their tour and it is this that Casals feels is missing among today's players.

"Without them [sponsors and promoters] there are no tournaments, and they're taking all the risks," the 74-year-old said. "I feel the women have to continue establishing themselves, yes, but also giving more.

"It's easy to take it for granted. I'm not saying all of them are blase about it, and I'm sure the WTA talks to them about what's important and what they need ... but most of the time you're talking to their agent.

"There's not enough closeness or relationship."

'There would be no women's game without the WTA'

By the time the players left the London hotel, they had installed King as president of their new organisation and her quest for equality gathered momentum, including the pursuit of equal prize money for women at Grand Slams.

"In my lifetime that could have been the most exciting year of my life," King told the Today programme's Karthi Gnanasegaram. "It was such a joyous moment that we know we were really together.

"We are the example [for other women's sports]. We showed them we could do it. If you can see it, you can be it."

The US Open became the first of the four Grand Slam tournaments to pay equal prize money to men and women in 1973, with Wimbledon the last in 2007.

Former British number one Laura Robson says the women's game would not have survived without the formation of the WTA.

"The Original Nine who kicked it off have given us all a chance to even have a job in the first place, a chance to work and earn money doing what we love - and that's playing tennis," she told BBC Sport.

"There would be no women's game without the WTA.

"You listen to Billie Jean King and the idea is to always keep pushing. We all realise what areas can continue to improve and get better and I'm sure the WTA is looking at the next 50 years and the next big plan because the game grows all the time."

In an open letter to the Original Nine to mark their 50 years in 2020, 2019 US Open champion Bianca Andreescu wrote: "I'd like to think that maybe other women along the way would have done the same thing, but the point is, you took the biggest leap, you did it first, and your generation has inspired mine to continue fighting and striving for change."