Not all Chinese nationals Romanize their names in Mandarin Pinyin. Exceptions include:
Ethnic minority names are often pronounced in the Romanization of their native languages, e.g., Aisin Gioro, Bat-Erdene, Mehmet, Tenzin, etc.
People in Hong Kong, Macao, and Taiwan regions often use different Pinyin systems, e.g., Cantonese Pinyin or Wade-Giles Romanization.
The names of Chinese nationals in the past may also be in different Pinyin systems, e.g., Mao Tse-tung (in Wade-Giles Romanization) is MaoZedong in Pinyin.
Some people have English given names or gave themselves English names. For example, Jack Ma and Jackie Chan (this Chan is Cantonese Pinyin; its Mandarin Pinyin equivalent is Chen).
Very occasionally, a non-traditional Chinese given name might have more than two syllables, but this might become more frequent in the future.
Some people in the past had a one-syllable given name and a two-syllable “style name” or “courtesy name”, often used interchangeably. This may cause confusion when reading classic Chinese novels or studying historical figures.