Orcs are brutish, evil beings, created for war. They delight in destruction. All their essence is bent towards violence, mind and body. They despise beauty and goodness, finding their very presence insufferable, and do all they can to burn what is right in the world to ash.
A typical orc has no real concept of loyalty, either familial or otherwise. It travels with a clan for the promise of war and plunder. If that is not forthcoming, or if a greater leader surfaces, an orc will change its affiliation in a heartbeat, serving whichever warlord, or ‘Krudger’ in their language, can promise the most bloodshed. So it is that tribes tend to be named for their current warlord, or favoured hunting grounds, and their banners bear simple motifs and colours which serve little purpose other than to provide a rallying point in battle.
– lore snippet from 3rd Ed. Rulebook