John Arbuthnot Fisher, 1st Baron Fisher, was a highly influential British admiral known for his efforts to reform and modernize the Royal Navy. He served as First Sea Lord for two periods, during which he championed technological innovation, most notably the introduction of the revolutionary dreadnought battleship. His reforms were instrumental in preparing Britain for the naval challenges of the First World War, though his tenure was also marked by controversy. Fisher's legacy is that of a brilliant, energetic, and often ruthless innovator whose impact on naval warfare was felt for decades.