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Herb Kelleher, who co-founded low-cost US carrier Southwest Airlines, has died aged 87, the company says.

The company described him as "a pioneer, a maverick and an innovator" who disrupted the airline industry "by making flying both fun and affordable".

He is survived by his wife Joan and three of their four children.

Founded in 1967, his airline initially aimed to provide cheap flights between the Texas cities of Houston, Dallas, and San Antonio.

However Mr Kelleher, who had trained as a lawyer, was forced to fight a legal battle after competitor airlines fought to prevent his planes from operating.

The Supreme Court of Texas eventually ruled in his favour and the airline began service in 1971.

"I knew nothing about airlines, which I think made me eminently qualified to start one," Kelleher told National Public Radio in 2016, "because what we tried to do at Southwest was get away from the traditional way that airlines had done business."

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Southwest offered cheap tickets in single-class cabins without reserved seats - tactics that became common in the airline industry several decades later.

The airline's business model, which also included shortened turnaround times at airports, cabin crew collecting rubbish, and high aircraft utilisation, has since been copied by other low-cost carriers including Ryanair of the Irish Republic and Easyjet of the UK.

Since its early days, Southwest has expanded to become the world's largest low-cost airline with more than 700 Boeing 737 jets making 4,000 flights a day, Business Insider reported.

"Herb's passion, zest for life, and insatiable investment in relationships made lasting and immeasurable impressions on all who knew him," Southwest said.

Many in the aviation industry have been paying tribute.