There are three different heroes you can use, these are listed below along with their strengths and weaknesses:
Lance
Lance is unlocked at the start of the game and is basically a melee bruiser with heavy armour. Lance is a good all-around choice, which makes him suited for beginners.
Stonelord
Stonelord is a healer so make sure you keep him in the thick of the action as much as possible.
Eris
This powerful female character is essential for end-game levels so make sure she stays alive by keeping her behind walls of Infantry Towers.
Note: Subsequent heroes unlock at Chapter 3 and Chapter 6.