Jaws as we know it owes its existence to producers David Brown and Richard D. Zanuck. In 1973, they somewhat serendipitously got their hands on an early copy of Peter Benchley's novel, Jaws. Both devoured it (#sorrynotsorry) in a single night and bought the film rights before the novel was even released to the public. Robert Brown would later say that if they'd read the story twice instead of just once, they would have realized what a pain it would be to make this film and probably bailed.
Jaws did indeed prove to be a hugely difficult movie to shoot, and there was tension between Brown, Zanuck, and director Steven Spielberg throughout filming. The movie was supposed to cost $3.5 million and take 55 days to shoot. But thanks to a constantly malfunctioning trio of mechanical sharks and complications from filming on the open sea, that's not quite how it went down.
Before it was all over, they'd spent $9 million and worked for 159 days. The crew and director all went a little nuts, and Spielberg lived in constant fear of being fired from the production. (Source.)
Despite the delays, Brown and Zanuck stuck with it and even convinced Universal Pictures to do something almost unprecedented at the time: They advertised the movie on television. Back then, that was a risky move. TV ads were expensive, and other experiments in TV advertising had flopped in the past.
But this time it worked in a big way. Their $9 million money pit ultimately raked in $260 million in the U.S. alone and basically invented the summer blockbuster. Brown and Zanuck went on to enjoy great success, though they never had another hit quite like Jaws. How could they? (Source.)