Hagranyms

The Orcs of the Grey Mountains call their special mounts Hagranyms. The Hagranyms are not animals; many are more intelligent than the Orcs riding them. This is one reason why all attempts by Bretonnians to tame them have failed; the Hagranyms refuse to cooperate and are clever enough to cause all kinds of problems. The other reason is that all Hagranyms are bloodthirsty killers, delighting in slaughter for its own sake as well as for food.

They have chosen to ally with the Orcs because it increases their chances for slaughtering something other than Orcs. Most Orcs think that they have tamed the Hagranym by their superior strength. Only a few of the most intelligent trainers have found that the creatures choose to cooperate. The Orcs know that the Hagranym are individually stronger, and it is only their belief in their intellectual superiority that sustains the relationship. If the Orcs find out that they are being manipulated, it will be war.

Source

 * Warhammer Fantasy RPG 2nd ED -- Knights of the Grail pg. 69