This portrait was eloquently described by Giorgio Vasari in his 1568 biography of Titian. He identified the man as a member of the Barbarigo, an aristocratic Venetian family.
The most likely candidate is Gerolamo, who was 30 years old in 1509. He had numerous political and literary contacts and would have helped the young Titian on his path to success.
The painting served as a model for the Self Portrait at the Age of 34 by Rembrandt.