Orunos is Midgard's terracite trophy mob. He's more difficult to kill than the corresponding mobs in the other realms, and his trophy is bigger.
When Orunos spawns he cons yellow or orange to 50 and has four adds with him. The moment you kill him he comes back to life as a purple cloud that casts disease. You have to kill this cloud to get his remains.
He's located at 27.6k, 18.5k in Midgard's Underground Forest.
Orunos's trophy was added to the game in version 1.75 on April 6, 2005. For a list of other trophies that were added at the same time, click here.