In just four years of operation, Uber has ignited a new global ride-sharing industry with the promise of transforming urban transportation and helping many people get by without owning cars.

But these days, the hot start-up is facing its toughest challenge yet — curbing its ugliest, most aggressive impulses before its win-at-all-cost culture begins to turn off investors, potential employees and the ride-hailing public at large.

The revelation, reported on Monday by BuzzFeed, that an executive publicly floated the idea of investigating the private lives of journalists who criticize Uber was only the latest in a parade of unflattering news about Uber’s tactics as it navigates the next phase of its growth.

Uber has grown into one of the most valuable start-ups in Silicon Valley, with outposts around the world. It has raised about $1.5 billion and is valued at more than $17 billion, with the inevitable talk of a public offering.