Final answer:
William Seward was the U.S. Secretary of State responsible for the purchase of Alaska from Russia for $7.2 million, an act initially criticized but later valued after the Yukon gold discovery.
Step-by-step explanation:
The U.S. Secretary of State who arranged to buy Alaska from the Russians for $7.2 million was William Seward. In 1867, understanding the strategic value and the resources like fish and furs, Seward negotiated the purchase which was later known by many as Seward's Folly. Critical opinion, however, shifted after gold was discovered, leading to the Klondike Gold Rush, and the acquisition was seen as a strategic boon, significantly increasing the United States' territory.
Despite the initial skepticism and criticisms from the press, dubbing Alaska as "Seward's Icebox", the purchase added nearly 600,000 square miles to the United States. This land offered rich mineral resources and proved to be of great importance for coaling stations for merchant ships in the Pacific. While William Seward faced initial mockery, the discovery of gold in the Yukon overshadowed the sentiments and justified the investment.