Gotrek Gurnisson is a famous Dwarf Slayer. He travels with his rememberer, companion and unspoken friend Felix Jaeger, a human poet from The Empire. In WAR, both these characters can be found in The Screaming Cat, a tavern in Altdorf. The exploits of Gotrek and Felix are detailed in the Slayer Series of novels started by William King and being continued by Nathan Long; published by The Black Library, the publishing arm of Games Workshop.
Gotrek committed a terrible deed in his younger years that cast shame upon his family and clan, causing him to renounce his former life as an Engineer and take up the Slayer Oath, to seek an honourable death fighting against monsters and other dangerous creatures. Gotrek is incapable of not giving his all to a task and sees it as dishonourable to simply let his opponents kill him. As a result, he has been so successful (or arguably, unsuccessful) in his quest for a heroic end that he has now been adventuring for over 80 years. Gotrek has the typical appearance of a Dwarven Slayer: heavily muscled and tattooed with a beard and hair dyed bright orange and spiked with pig grease. He is missing an eye which was lost in a battle with a horde of Greenskins that he and Felix Jaeger battled in the Border Princes.
Some decades into his travels, Gotrek saved Felix Jaeger from being run down by the Emperor's cavalry during the infamous Window Tax Riot of Altdorf. In an act of drunken stupidity, the young poet swore to accompany the Dwarf on his travels and to write an epic poem about him once he was dead. Though Felix claims to regret this, each chapter of a Slayer novel begins with an excerpt of the text "My Travels With Gotrek", supposedly the result of this oath and implying that at some point, Gotrek finally meets his fate. Luckily (or unluckily for Gotrek) this has not yet happened in WAR.
Traveling together, the two adventurers met a half-mad Dwarf that told them of a vast treasure guarded by the largest troll ever seen. The Dwarf said that the creature and the treasure lay underneath the Orc-infested halls of Karak Eight Peaks, a lost hold of the Dwarves which fell thousands of years ago. The duo traveled to the fallen hold and with the help of some adventurers on the road, they were able to find and slay the troll. Felix Jaegar gained his magical dragon slaying sword, named Karaghul, from the pile of treasure that the creature guarded.
Though the exact nature of Gotrek's crime is never stated, the story Beastslayer features a Chaos Lord of Tzeentch requesting a vision of his twin sorcerers. After a scene depicting Gotrek's acquisition of his axe, the next scene involves Gotrek returning to a burning village, ending as it focuses on the corpse of a Dwarf woman and her baby. The next scene depicts Gotrek in the throneroom of a Dwarf hold, arguing with a Dwarf lord. Though no dialogue is given, the lord's guards attack Gotrek, resulting in the slaughter of virtually every Dwarf present in the chamber. The scene finishes with Gotrek shaving his head with a knife, probably giving in to the Slayer lifestyle.
Since embarking on his death quest, Gotrek has become a master warrior (and to some degree, so has Felix). The length of their lives and the dangerous quests and battles the duo constantly has faced, has given them vast experience and has honed their fighting skills to a razor's edge. Together they have slain dragons, sorcerers, a Bloodthirster of Khorne, two of the most powerful Tzeentchian sorcerers in existence, and just about every kind of monster imaginable, and yet they live on. The axe that Gotrek carries has slowly changed him into the epitome of Dwarven strength and stubborn vitality. He is undoubtedly one of the greatest and maybe the greatest living Dwarven warrior to be found. Gotrek laments constantly that he cannot find a beast or challenge great enough to slay him, but his problem mainly comes about from the simple fact that his ablities put him on par with beings such as Malekith, Daemon princes, Tyrion commanders of the Elven armies, Grombrindal the White Dwarf, Kurt Helborg, Lord of the Reiksguard, and Greater Daemons of Chaos. Most other creatures and warriors simply do not have the skill neccesary to best him. His friend Felix is (ironically) constantly complaining to himself that if Gotrek is ever slain, he himself will be killed by the same enemy shortly thereafter.
Gotrek wields an enormous battleaxe, forged of starmetal and imbued with immense magical potency by ancient Dwarf Rune magic. He gained this weapon during his excursion into the northern Chaos Wastes, where he recovered it from the body of the dead son of King Thangrim Firebeard. The Elven Mage Teclis once read the magical aura of Gotrek and determined that immense power was flowing from the axe and subtly changing the Slayer into something greater than an ordinary Dwarf. In the book Elfslayer, Max Schreiber notices that after 20 years of adventuring, neither Gotrek or Felix seemed to have aged, and that they seem to recover quickly from wounds. It is hinted that both Gotrek and Felix have become altered by being in the proximity of the runed axe, granting longer life, greater reslience, etc. It is strongly implied that Gotrek's axe once belonged to Grimnir, Warrior God of the Dwarfs.