Elon Musk, the world’s wealthiest person and the country’s biggest political donor, said on Saturday that he would create a new political party, an enormous and challenging undertaking that would test the billionaire’s newfound influence on American politics.

“When it comes to bankrupting our country with waste & graft, we live in a one-party system, not a democracy,” Mr. Musk wrote on X, his social media website, on Saturday. “Today, the America Party is formed to give you back your freedom.”

Mr. Musk, once a close ally of President Trump’s who in recent weeks has repeatedly bickered with him, had not filed paperwork as of Saturday evening for the new party, though he added in a separate post that the America Party would be active in elections “next year.” Any new party would be required to be disclosed to the Federal Election Commission.

Even as Mr. Musk has proved that he is willing to use his resources to move quickly and dramatically, he also has a long history of not following through on promises.