Who is the current Chief Justice of the United States?

The current Chief Justice of the United States is John Roberts. Roberts was appointed by President George W. Bush and took his oath of office on September 29, 2005. As Chief Justice, he presides over the Supreme Court's sessions, leads the business of the Court, and is responsible for maintaining the Court's integrity and public trust. His role includes deciding cases, guiding the Court's agenda, and ensuring the efficient administration of justice.

In contrast, Ruth Bader Ginsburg served as an Associate Justice until her passing in September 2020, and Clarence Thomas is currently serving as an Associate Justice but has never held the position of Chief Justice. Anthony Kennedy also served as an Associate Justice until his retirement in 2018. Thus, they do not hold the office of Chief Justice, confirming that John Roberts is the correct answer.