SHANGHAI — “Mickey Maose” has officially arrived.

In a rain-dampened ceremony attended by Chinese dignitaries, the Walt Disney Company on Thursday opened its $5.5 billion Shanghai Disney Resort, a theme park and hotel complex that represents a hard-fought victory in China for the singularly American entertainment conglomerate. “Our dream comes true,” a beaming Robert A. Iger, Disney’s chief executive, said in Mandarin at the ceremony’s start.

The park — Disney’s first on the Chinese mainland — was held up as nothing less than a historic symbol of United States-China relations. Mr. Iger read aloud a letter sent by President Obama that heralded the resort as capturing “the promise of our bilateral relationship.” In a letter of his own, China’s president, Xi Jinping, called the project, which took nearly two years of bruising negotiations to realize, a sign of China’s “commitment to cross-cultural cooperation and our innovation mentality in the new era.”

On a lighter note, Wang Yang, one of China’s vice premiers, stood onstage in front of the park’s lavish storybook castle and joked that the rain was a sign of good luck — the “rain of U.S. dollars and RMB,” he said, referring to China’s currency, the renminbi. Disney owns 43 percent of the resort, with the majority stake held by a Chinese state-controlled consortium.