The friendship developed into a partnership. Mr. Levandowski left Google last year to form Otto, a self-driving trucking start-up. Uber acquired it months later for nearly $700 million. Mr. Kalanick subsequently appointed Mr. Levandowski to run Uber's autonomous vehicle research.
That relationship has since set off a legal morass, with Google's self-driving vehicle business — now called Waymo — accusing Mr. Levandowski of creating Otto as a front to steal trade secrets from Google, then using the findings with Uber's driverless cars. On Monday, a federal judge in San Francisco barred Mr. Levandowski from working on a crucial component of Uber's self-driving car technology for the duration of the case.
The implications are set to reverberate far beyond the courtroom. Any setback for Uber will shake up the driverless car industry, which is locked in a bitter race to introduce and commercialize autonomous cars. Silicon Valley tech titans and Detroit automakers are making huge investments — bets that autonomous vehicle technology will usher in a new age of how people get around. For some companies, especially traditional carmakers, their very survival is at stake.
While Google has been developing autonomous vehicle technology for more than a decade, others have raced to catch up. General Motors, Ford, Apple, Tesla, Volkswagen, BMW and Mercedes-Benz are among those that have jumped in. All are competing — and sometimes cooperating — for a slice of a new market expected to top $77 billion over the next two decades, according to a study from Boston Consulting Group.
Uber has been ahead of many others in publicly testing autonomous vehicles. Last year, the company began a pilot program of autonomous cars in Pittsburgh; it has also done testing in San Francisco and Tempe, Ariz.
That aggressiveness has spurred an intense rivalry with Waymo. Waymo's legal pursuit of Uber and Mr. Levandowski is out of corporate character; Google has tended to refrain from suing former employees who move to competitors. Many at Google and Waymo are incensed at Mr. Levandowski and how he may have betrayed them for a rich payday, according to current and former employees.
That has pushed Waymo to strike back. Beyond suing Uber, Waymo said on Sunday it had teamed up with Lyft, a ride-hailing rival, on driverless car initiatives.
"This is a race where every single minute seems to count," said Carl W. Tobias, a professor at the University of Richmond School of Law, who has followed the Waymo-Uber case.
Uber and Waymo declined to comment for this article.
Uber and Google once considered each other allies. Google's venture capital arm, now known as GV, spotted Uber's potential early and invested more than $200 million in the fledgling ride-hailing network in 2013.
David Drummond, then Google's chief legal counsel and an early Uber enthusiast, took a seat on Uber's board. At one point, Google promoted Uber as a transportation option in the Google Maps app, and Uber drivers relied on Google Maps.
But the relationship crumbled as the two companies' paths converged. Google began testing its own car-pooling service inside Waze, a mapping app it owns. Uber eventually moved away from relying solely on Google Maps.
A week after Uber acquired Mr. Levandowski's start-up last August, Mr. Drummond, who had become chief legal officer of Alphabet, Google's parent company, stepped down from Uber's board.
At the same time, Uber ramped up its own driverless car efforts. In 2015, Uber opened the Advanced Technologies Center in Pittsburgh, home to its self-driving work. It hired Brian McClendon, Google's head of maps, and brought on staff members from Carnegie Mellon University.
Around then, the friendship between Mr. Levandowski and Mr. Kalanick deepened, according to people close to both men. After "jam sessions" between the two — essentially brainstorming meetings where they would walk and talk over the future of driving — Mr. Kalanick's pedometer would clock in with thousands of steps.