What is William seward most famous for?

William Seward is most famous for serving as the U.S. Secretary of State under Presidents Abraham Lincoln and Andrew Johnson. He is particularly noted for his role in the acquisition of Alaska from Russia in 1867, often referred to as "Seward's Folly" at the time, which later proved to be a significant expansion of U.S. territory. Additionally, Seward was a key figure in the anti-slavery movement and played a vital role in shaping foreign policy during the Civil War era.