Who was florida's first governor?

That depends on when you are referring to.

The first military governor was Andrew Jackson (March 10, 1821 - December 31, 1821).

The first governor of the Florida territory was William Duval (April 17, 1822 - April 24, 1834).

The first governor of the state of Florida was William D. Moseley (June 25, 1845 - October 1, 1849).