A free app for Android, by EC Game.

Empires Calling: Kings War is a free strategy game that lets you play the role of a medieval king or a leader who must build an empire and fight against other players who are also trying to rule the world.

The game is set in the medieval period, and it takes place in a world that has been destroyed and is in the middle of a long war.  You can build an empire by recruiting legendary heroes and building a medieval kingdom, and you can fight against other players by building a fortress and attacking them.