They are the fists of the Warchief, whoever he is. They are the sworn honor guard, the advance force, the first into the fray and the last to leave. They are Kor'kron. What other forces in the Horde can aspire to be they have already been. Since the founding of Orgrimmar, they have advanced the cause of the Horde anywhere the battle has been joined, fighting against Illidan's forces in Shadowmoon Valley, pushing against the Lich King in Northrend, throwing the traitorous Varimathras back to the pit in Undercity. Now you can find them seeking to drive the humans into the sea on the new islands near Vashj'ir or fighting the Twilight's Hammer in the Highlands.
They are Kor'kron. They know only victory or death. Their loyalty is absolute.
Quellers of the recalcitrant
The Kor'kron appear to us first after the formation of Orgrimmar and the nation of Durotar. They are not notably present during the battles with Daelin Proudmoore and his forces, but clearly the genesis for their creation must derive from that time, for they appear fully formed and ready to defend the Warchief when the original storyline of World of Warcraft debuted. Since we know that the Horde formed by Thrall after Doomhammer's death was in constant conflict from that time through the landing in Kalimdor and the Battle of Mount Hyjal and then the founding of Durotar, it seems apparent that the nucleus of the Kor'kron was in the battle-hardened veterans of the period.
Some indicate that the Kor'kron are a far older order, tracing their roots to the pre-Horde Orcs of Draenor, whose traditions Thrall found while studying the rise and fall of his family's bane, Gul'dan the warlock. Whether or not that is so, Thrall made the Kor'kron something new, a force owing no allegiance to clan or clan lord but loyal to the Horde itself and its Warchief over all other concerns. Shaped by Thrall's desire for a force that would not be beholden to any petty leader, during the time when the young shaman was forced to try and forge a new nation, the Kor'kron serve the Horde directly, under the leadership of their High Overlord, Varok Saurfang.
Above all, the Horde
This unity of purpose and abandoning of clan loyalty has made the Kor'kron unique among Orcs, and as such, unique among the Horde. When the Warchief needed someone to take and hold an advance position against not only the Burning Legion but also Illidan's forces, he sent the Kor'kron under Overlord Or'barokh, and the Kor'kron did it. There was no squabbling over honor, no misplaced pride, no disputes over what was glorious and what was not. The Kor'kron believe that honor and victory are predetermined for them by their obedience to the Warchief. They don't need to dispute over it; they simply need to execute. In a military machine so often defined by the need for personal honor, the Kor'kron have eschewed it.
In an organization so often obsessed with personal glory, the Kor'kron have abandoned it. As a result, they have become preeminent in the wars the Horde has fought over the past 10 years because they can always be trusted to put the objective ahead of themselves. When the Horde Expedition went to Northrend, the Warsong fought for Garrosh Hellscream, their hereditary clan chief, but the Kor'kron fought for the Horde and the Warchief, and Hellscream because he was the Warchief's representative. Now that Hellscream is the Warchief, they fight directly for him, but only because he holds the office. This loyalty not to any person but to the position makes them immune to the politics that plague other organizations.
Simply put, the Kor'kron are the Horde's ultimate elite force. When High Overlord Saurfang was forced to put down the creature that wore his own son's face, it was the Kor'kron who rode into battle with him. They do not falter; they do not put themselves before the Horde. They do not defy or fail the Warchief or the High Overlord. Theirs is victory or death. This is not always ideal, however, as even their own High Overlord himself put it:
The Kor'kron walks this knife's edge more than any other force in the Horde. They are most often called upon to be the sharp point of the wedge, the first to ride forth and deliver the Warchief's will. Having surrendered their clan identities and personal aspirations to the Kor'kron, they must be able to trust their leaders to display honor and integrity, or they risk falling into the same trap as the old Horde, becoming tools of those unworthy of them.
With Warchief Hellscream's different vision for the Horde, often it is the Kor'kron who must enforce his will, especially when others have failed him so miserably. It has been the Kor'kron who led the assault upon the new islands off the shores of the Eastern Kingdoms and who learned the true nature of the Naga assault for the Horde, and it was the Kor'kron who crewed the airships that brough the Horde in force to the Twilight Highlands. Wherever and whoever the Horde now fights, the Kor'kron exist to ensure that the Warchief's will, and not that of generals who overreach themselves or clanheads with different agendas, is absolute. If the eyes of Hellscream are always upon you, then the Kor'kron exist to be his fists.
Be not fooled, however. The Kor'kron do not serve Hellscream; they serve the Warchief, whoever he or even she is, and through the Warchief, they serve the Horde. They have fought from Silithus to Northrend, from Outland to the Highlands. Whenever the Horde needs them, they are there.
Next week, the 7th Legion.
While you don't need to have played the previous Warcraft games to enjoy World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the World of Warcraft in WoW Insider's Guide to Warcraft Lore.