Who became the first president to be impeached?

Andrew Johnson became the first president to be impeached in 1868. His impeachment arose primarily from political conflicts following the Civil War, particularly regarding his violation of the Tenure of Office Act, which was an attempt by Congress to restrict the president’s power to remove certain officeholders without Senate approval. Johnson's presidency was marked by profound disagreements over Reconstruction policies and his lenient approach towards the Southern states after the war.

While other presidents, such as Bill Clinton and Richard Nixon, also faced impeachment processes, Johnson's was significant as it set the precedent for the impeachment of future presidents. Nixon famously resigned before an impeachment vote could take place, and Clinton was impeached but acquitted by the Senate, making Johnson's impeachment distinct in being the first instance of the formal impeachment process being initiated against a sitting president. Ulysses S. Grant, although a prominent president during that era, was not impeached and faced no similar proceedings.