Who is Johanna Mason from Catching Fire and what is their importance?

Johanna Mason is the female tribute from District 7. Johanna makes fun of Katniss after the opening ceremonies by riding the elevator up to her floor naked. Later Johanna makes a show of wrestling naked, hoping to make Katniss uncomfortable. However, in the arena, Johanna makes herself an ally of Katniss by bringing her two tributes she was told Katniss needed to survive. Katniss later learns that Johanna was part of a plot to save Katniss's life and that it was her job to remove Katniss's tracking device before the force field went down in order to keep the Capitol from easily tracking her. Johanna dies protecting Katniss from several other tributes.