Dire orc

Dire orcs, also known as berserkers, abominations, horrors and brutes, are heavily mutated orcs. Dire orcs are created through blood rituals, though the Twilight's Hammer seem to know how to create them as well; it is unclear if the Twilight's Hammer has their own methods or have adopted the Bleeding Hollow's.

History
The first dire orc was seen in the Black Temple — Gurtogg Bloodboil, a leader and presumed member of the local Bonechewer clan fel orcs. After the Cataclysm, Raz Skullcrusher was captured by the Twilight's Hammer and empowered into a dire orc by magic energies. Later, a group known as the Dark Shaman tried to recreate the Twilight ascension process, but the experiment failed and resulted in Lava Guard Gordoth becoming transformed into a dire orc or rather, mutated into a "hideous form".

In Mists of Pandaria, Garrosh Hellscream was in need of a subject to be infused with the powers of Y'Shaarj. Out of sheer loyalty, Malkorok volunteered and was twisted into a hulking, mutated orc.

In Warlords of Draenor, Grulkor investigates a fungal infestation in the Mistcreep Mire located on the east coast of Gorgrond. Throughout the quests he slowly becomes more and more obsessed with trying to harness the power of the mushrooms in the mire, eventually leading him to absorbing the power of a strange fungus. After consuming all the different mushrooms found in the mire as well as the strange fungus, all the spores eventually overtook his mind and mutated his body into a hulked orc monstrosity; causing him to attack the adventurer.

Additionally, in Tanaan Jungle and within the Stygana Cavern, the Bleeding Hollow Clan and their herbalists are experimenting with infusing orc brutes with mushrooms, affecting them similarly to Grulkor in Gorgrond. There are also several failed experiments laying dead on the ground nearby. An alternate version of Gurtogg Bloodboil is also encountered, and killed, in Hellfire Citadel.

There exist dire pale orcs as well. They are created through the Ritual of Destruction.

Notes and trivia

 * The name "dire orc" is taken from the game files as no other name is known. Technically, the model name is "felorcdire", but not all of them are fel orcs. In Warlords of Draenor the dire orc model is named "hulkedorc" & "felorcbrute" for the dire fel orcs.
 * Although it seems most NPCs and spells referring to dire orcs since Warlords of Draenor are hinting towards "hulked orc" being a more proper name, as it is also the name of the model.
 * There is not a single mention of what dire orcs are actually called. All quest text and adventure guides avoid referring to them as dire orcs, preferring names and derogatory terms like "abomination".
 * Pre-Warlords of Draenor dire orcs use the same skeleton and animation as wights (which was also formerly used by dire trolls prior to patch 5.2.0). Dire orcs in Warlords of Draenor and after instead use the new dire troll skeleton.
 * Gul'dan in Nighthold turns into an appearance that is similar to a dire orc.

Speculation

 * The Bonechewer Behemoths of the Black Temple may be different forms of dire orcs.
 * Some infested orcs are much larger and more heavily mutated than others, as such they may actually be some form of plant dire orcs as they have similar traits. Heavily mutated by flora (similar to mushrooms in Gorgrond and Tanaan Jungle) resulting in huge, hideous abominations.