Orruks are generally known as big, nasty brutes. So, the ones in charge tend to be even bigger and nastier. Add to it that they often ride even biggerer and nastierer brutes into battle and you have yourself the Killaboss. We get a look at the one coming in Dominion, the new starter set for the new edition of Age of Sigmar in this preview.
From the article:
While the Kruleboyz are known mainly for their cunning schemes and sneaky tactics, the orruks that survive long enough to claim a position of authority grow much taller and stronger than the rest of their kind. They become so strong, in fact, that they can even take down one of Sigmar’s champions, which you may have witnessed in the new edition’s phenomenal cinematic trailer.
Known as Killabosses, these leaders rule their tribes with an iron fist, always looking out for the next aspiring usurper aiming a stikka at their back.* When they ride to war, they often do so on the back of a vicious canine monster called a Great Gnashtoof, which is capable of tearing off an ogor’s head in one swift bite. This makes these units even more fearsome combatants than usual, as their foes come under a hail of razor-sharp strikes from fang, claw, and stikka while the boss on top issues all kinds of cunning commands.