Who is Commodore George Dewey from The Rise of Theodore Roosevelt and what is their importance?

Shortly after becoming assistant secretary of the navy, Roosevelt endorses Commodore George Dewey as the man in charge of the Pacific naval forces. The appointment requires some political wrangling, but, in true Roosevelt fashion, he wins the battle in the end.

When Roosevelt begins to sense war is near, he sends telegraphs to Dewey, to prepare for battle in the Philippines. After the victory, Dewey credits Roosevelt's early warning.