Pvt. Johnson is retired US Navy Seal, who decided to Join the Army, because he couldn't live without some aspect of the Military. He was only 25 when the outbreak happened, and was with the Hangar crew.
John was with the troops at the USARMY Base until the battle at the steel mill, with all the season one characters. He fights the horde of zombies off with Cpl. Riley and Pvt. Parker.