a) William Howard Taft

William Howard Taft, the 27th President of the United States, was the only U.S. President to later serve as Chief Justice of the Supreme Court. After his presidency, Taft achieved his lifelong ambition by being appointed Chief Justice in 1921, a position he held until 1930. His unique career path reflects his deep commitment to law and justice. As president, Taft focused on trust-busting and expanding U.S. influence abroad, but he is often more highly regarded for his contributions to the American legal system as Chief Justice.