Thief

The thief is the worst fighter of all the heroes. He will just mess around and throw some coins. If he survives long enough, he will give you a Red Diamond.

Pros

 * Give some gold,
 * Can crit.

Cons

 * Low HP.

Tips

 * Thieves are best when you've already cleared the level, they won't die (except if they go for traps) and they will give you some gold and the Red Diamond.