Haargroth the Blooded One is a Chaos Lord of Khorne created as part of the fluff surrounding the release of Warriors of Chaos during the early "Hordes of Chaos" approach and as part of the build up to the Storm of Chaos campaign. He is one of the Lieutenants of Archaon.
Appearing in White Dwarf #271, Haargroth was once a humble orphaned peasant boy from a Norscan tribe (unindentified in the original article, but later claimed to be the Graelings), who was scorned and abused by all of the other villagers due to the death of his parents. Somehow, Haargroth survived being beaten by the other youngbloods whenever they pleased and being forced to root amongst the scraps for his sustenance, but needless to say, this built a huge well of rage within him. One summer, when the rest of the tribe went raiding, Haargroth was left behind to watch the goats, when a beastman stole and ate one of them.
For Haargroth, this was the last fucking straw. He tracked the creature down by the trail of blood it left, and found it asleep. A voice whispered in his head and he listened to it; grabbing the beastman's axe, the beast woke and threw itself at him. The once-victim struck it dead with one chop and went mad, hacking it into a bloody carpet. Enfused with a sense of power at last, Haargroth barely noticed the axe starting to get shinier looking.
Wandering in a daze back to his village, Haargroth only noticed the two guards when they approached him, and he killed them both in one blow. None of the other villagers remaining dared to challenge him, so Haargroth walked right into the longhall, sat his ass in the chieftain's chair, and ate and drank whatever he wanted, whenever he wanted for the rest of summer. When autumn came, and the raiders returned, the old chief was livid when he saw the former peasant sitting on his own chair. So Haargroth killed him too.
None of his tribe liked serving Haargroth, at first, but when the winter raids came and a rival village attacked, it was Haargroth who was the first to attack the raiders, butchering everything he laid eyes on and rallying his new tribe. Now they welcomed him, and Khorne blessed him, making his body swell with muscles and power, completing the transformation of his first weapon into a mighty Axe of Khorne.
Haargroth's tribe used that winter to conquer and crush every village they could find, brutally slaughtering all but the strongest warriors, even when their foes surrendered; for this, they became known as the Slaughterers. Over the years, Haargroth's tribe grew larger and larger, but his ambition never dimmed. Eventually, took them northwards, into the Chaos Wastes, conquering yet more, until finally he roared a challenge to Khorne to present him with a worthy foe.
And that was when Khorne threw Archaon at Haargroth like a cheap DM using a random encounter. Archaon tanked the best shot Haargroth could throw at him and then beat him into the ground with one blow, demanding Haargroth shut up and obey him. Since that day, Haargroth has followed Archaon, leading his army into the thickest and fiercest battles he can, hoping to one day get strong enough to challenge and defeat the Everchosen himself.
According to the post-campaign fluff for Storm of Chaos, if anyone paid attention to it anyway, Haargroth was eventually killed by Ar-Ulric.
Haargroth was unique amongst his fellows in that he didn't use the new (Aligned) Chaos Champion model with some attendant fluff; instead, he was given a custom model that was basically an old-timey Bloodletter champion model with the head of 3rd edition Archaon and the arms of an Orc. Hence his picture up at the top of the page here.