Didi means "beep-beep" in Chinese. Originally, the name was intended to convey the sound of a friendly hello.
For Uber these days, Didi might sound more like: "Move out of the way. I'm going to blow past you."
Didi Chuxing, China's fast-growing ride-hailing service, is quietly amassing the money, expertise and allies it will need if it decides to enter the U.S.
Why should Uber be worried?
Economies of scale: Didi has become the world's largest ride-hailing company, and it's not even close. Uber and Lyft combined handle 70 million bookings per month. Didi alone gets 600 million. That's a stunning number for a company that got started in 2012.
Driven leaders: Company founder Cheng Wei is an intensely competitive 34-year-old chemistry major from a small town in mountainous south central China. In 2014, Cheng brought Jean Liu on board as president. Liu, 39, formerly a Goldman Sachs banker and Harvard grad, knows how to win investor confidence.
Deep pockets: Tencent and Alibaba, China's two most valuable companies, have invested in Didi. Another big-name backer is Apple Inc., which bought a $1 billion (6.9 billion yuan) stake last year.
China monopoly: Didi controls 88 percent of China's ride-hailing market, giving it near-total dominance of its home turf.
You might recall that Uber had grand plans to conquer China when it entered that market in 2013. But Travis Kalanick & Co. were forced to capitulate last summer.
The battle was painful. Both companies lost billions of dollars subsidizing rides. In the end, Didi won a short and nasty war of attrition and Uber's China business was folded into Didi's.
Throughout the clash, Cheng exhorted his employees to hold their ground against Uber: "No Chinese Internet company on Chinese soil has ever lost to foreigners and Didi will not be the first!"
Didi Chuxing was formed in 2015 from the merger of ride-hailing rivals Didi Dache, backed by Tencent, and Kuaidi Dache, backed by Alibaba. They joined to launch a counterattack on Uber.
Leaders in Beijing, eager to exert maximum Chinese control over Internet-based businesses, gave their blessing to the marriage.
At the time of the merger, Beijing-based Didi Chuxing was valued at $6 billion. Today, the value is $50 billion, making Didi the world's most valuable startup after Uber. Lyft, with a $7.5 billion valuation, looks tiny by comparison.
So what's next for Didi?
Cheng and Liu make no secret about their plans. This month, the company raised $5.5 billion to "pursue global expansion and self-driving technologies."
And where better to pursue those goals than in America?
Didi moves fast. In March, the company opened an r&d center to develop self-driving cars in Mountain View, Calif. , home to Apple headquarters.
That same month, Didi hired Charlie Miller away from Uber to lead its safety and security team. Miller made headlines when he successfully hacked and remotely controlled a Jeep.
Keep your eye on Didi Labs. Ride-hailing services such as Didi, Uber and Lyft are likely to provide the first real-world test of self-driving vehicles.
These companies are willing to pay extra for self-driving technology — which initially will be pricey — because they can dispense with human drivers.
And if you are Apple CEO Tim Cook, you can let a trusted partner beta test your self-driving technology without having to paste your Apple logo on the grille.
Clearly, the war between Uber and Didi is not over. The battleground has simply shifted from China's East Coast to America's West Coast.
Roles have shifted, too. This time, Didi is the attacker. Uber finds itself on the defensive, distracted by intellectual property lawsuits, sexual harassment claims and the new alliance between Lyft and Waymo.
One other important difference: Uber did not have many friends in China. By contrast, Didi is tight with Apple, the world's most valuable company. And Didi is a major shareholder in Lyft — and Uber as well, for that matter.
As part of their peace agreement in China, Didi acquired a $1 billion stake in Uber, while Uber gained a 20 percent share of Didi.
But this seems more like a temporary truce than a permanent treaty. Cross-ownership simply gave Uber a way to unwind its Chinese operation. Both companies still want to be No. 1.
Cheng, Didi's founder, was proud to say that no Chinese Internet company had ever lost to foreigners on Chinese soil. Will Didi be the first Chinese Internet firm to triumph on American shores? Beep-beep!