The Leader/Commander of the Uruk-hai warriors was Saruman who's power leashed fear throughout all lands. The Uruk-hai are the product of Saruman's attempts to create a fighter that improved on Orcs by being far stronger and unaffected by sunlight. It is theorized that they resulted from breeding of Orcs and Men. There were also apparently Uruk-hai in Mordor in the service of Sauron, although these don't seem to appear onscreen in the films. It is unknown whether these Uruk-hai are directly related to Saruman's breed of Uruk-hai.

In This Clan We are the strong the powerfull we are URUK-HAI

This is our land and anyone who passes will die without any reason or cause. We will keep peace with others untill ordered to attack and cause Havoc on others.