There are four Leaders that players can obtain to help do supply runs and defend the Town during the Zombie Attack. You can upgrade these leaders using the medals you can get through Leader sales in shop, strongboxes and in the Arcade. 

• Jess;
• Ivan;
• Dakota;
• Nathan.

Each Leader has a special perk that will aid you in Supply Runs. To learn more about the perks at a certain level make sure to check the Characters button > Leaders > Tap on the certain Leader > check out their Rank and special bonuses they have. 

Using medals to rank up a Leader will make them stronger. 
You can use Survival Guides to increase their experience.