Who is currently the Chief Justice of the United States?

The correct answer is John Roberts. He has served as the Chief Justice of the United States since September 2005, after being nominated by President George W. Bush. In his role, Roberts leads the operations of the Supreme Court, oversees its sessions, and plays a critical part in the court's deliberations and decision-making processes. His leadership often influences the direction of the court, particularly in cases concerning key constitutional issues.

The other options mentioned are no longer the Chief Justice. Ruth Bader Ginsburg served on the Supreme Court until her passing in September 2020 and was known for her strong advocacy for gender equality and civil rights. Clarence Thomas is an Associate Justice and has been on the court since 1991, but he is not the Chief Justice. Anthony Kennedy retired from the court in July 2018 after serving for over three decades, making significant contributions as a swing vote on many landmark cases.