Who is speaking at the U.N. General Assembly, who isn’t — and why does Brazil go first?

Several prominent leaders will deliver in-person addresses at the U.N. General Assembly meeting on Tuesday, including President Jair Bolsonaro of Brazil, an avowed Covid skeptic whose mismanagement of the pandemic threatens his political future. Mr. Bolsonaro also has created a stir by vowing to defy the meeting’s vaccination requirement.

Many leaders are opting to use prerecorded video, as was done last year, or to have a lower-ranking representative speak in person, and the absence of a particular country’s leader this year can send a message.

Perhaps the most prominent leader to skip a personal appearance at the General Assembly is President Xi Jinping of China, an increasingly important financial contributor to the United Nations and a rival with the United States for influence there, an underlying source of tension.

Mr. Xi originally intended to have his deputy prime minister represent China, but in a last-minute change posted Monday by U.N. officials, Mr. Xi will address the General Assembly by prerecorded video as the last speaker on Tuesday.

President Vladimir V. Putin of Russia will not attend either, and his foreign minister, Sergey V. Lavrov, will speak instead.

In what may be another sign of France’s anger at the United States over a secret arms deal with Australia, the French president, Emmanuel Macron, has abandoned the idea of speaking at the gathering even by video. Instead he tapped his foreign minister, Jean-Yves LeDrian, to speak, which now could happen on the final day.

Iran’s new president, Ebrahim Raisi, also sent a prerecorded speech, skipping the opportunity for personal diplomacy that could help save Iran’s near-moribund nuclear agreement with major powers.

Mr. Bolsonaro will be the first head of state to address the gathering. Brazil has spoken first since the mid-1950s, and U.N. protocol officials say that the tradition began because at the time no other country’s leader was willing to take on that role. That position is now considered a coveted slot that can help set the tone of the week.

Among the other first-day speakers are the presidents of Turkey, Mexico, South Korea, Poland and the Democratic Republic of Congo.

The order of speakers generally adheres to the principle that the leader of the host country goes second, followed by other heads of state, heads of government, vice presidents, crown princes, foreign ministers, then deputies and ambassadors. It is also determined by the date when each of the 193 members makes the request.