Heroes are high powered troops in Clash Of Clans. They can not die and have a lot of hitpoints and health. You can use them in attacks or let them defend your village. Once a hero is beaten it goes to “sleep” for a while. After this sleep you can use him or her again.
The heroes cost dark elixir to build and to upgrade. They both can get up to level 40 in which they are extremely powerful. You should always upgrade your heroes to an acceptable level to make use of their powerful attacks.