Kastenessen (lit. "box-eater" (!!!) from the German) was originally a member of the mysterious faery folk known as the Elohim. He was of considerable high status, even amongst that élite crowd - if one were looking for a human equivalent, he'd be the all-star quarterback in a high school filled with nothing but the most over-privileged of kids.
Infelice, queen of the Elohim, spent millennia artfully and sophisticatedly flirting with the hunky Kastenessen. Just imagine her disappointment when Kasty, who, despite being held in such high regard by one and all, was not blessed with a huge amount of brains (okay, okay, if truth be told, he was not much more than a dumb jock who could only think with his exquisitely toned muscles), took himself off one day to start dating a human princess named Emereau Vrai.
The entirety of the Elohim were shocked at such a blatantly uncool act - a human of all things? How inelegant! How unfashionable! Infelice was of course also furious enough to spit, although needless to say she was very careful to internalise this rage, lest it should cause the faintest of cracks to show in her perfect façade of elegant and insouciant coolth. A search party was sent out to arrest Kastenessen and bring him back in arcane chains to hear the judgement of his peers. This they succeeded in doing, but not before Emereau Vrai had given birth to the merewives as a result of her union with Kasty. The birth must have come as a bit of a shock to both Emereau and her midwife, since merewives are malign marine creatures - imagine a permanently pissed-off mermaid and you'll be close to the truth. As an aside, this union makes Kastenessen a direct ancestor of Mr. Split Personality himself, Esmer.
When Kastenessen was eventually ferried back to Elemesnedene, the Elohim isle, he was immediately sentenced for his heinously inelegant actions to become an Appointed, because a peril had arisen in the far north of the world that the Elohim presciently foresaw might one day cramp their style. So Kasty was given a security guard's uniform (with nametag), a torch and a baseball bat and ordered to spend all eternity guarding the mouth of a huge eldritch volcano at the North Pole to stop any fiery serpents (known as skurj) escaping and ravaging the world. This harsh sentence was known as the Durance.
After eons being bored out of his tiny wits sitting all alone at the crater mouth of an active volcano, with absolutely nothing to do except smack the occasional presumptuous skurj across its magma muzzle with his baseball bat, Kastenessen finally snapped. He tore off his night watchman's costume and, calling upon his innate theurgy, sorcerously merged skurj essence into himself, a thing which fed his incandescent rage and sense of injustice even further (well, if you suddenly acquired molten lava for blood, you might experience episodes of short temper too). Then he summoned the skurj to leave their volcanic home and go ravaging across the entire earth while he too set forth to cause ruin and mayhem.
Despite by this stage having been driven barkingly mad and being hell-bent upon achieving nothing but destruction, Kastenessen did surprisingly then make one friend, namely Roger Covenant. These two seem to have experienced a bit of a bromance, swapping hands with each other by means of a little magical transplantation.
Kastenessen eventually lost his grafted human hand, courtesy of an altogether more primitive form of surgery performed by the Giant, Lostson Longwrath and shortly afterwards he was reluctantly persuaded to start attending relationship counseling sessions with Infelice, who still harboured a secret crush on the big bozo.
Appearance and Personality
Kastenessen originally typically manifested himself as a young Adonis with a perfectly sculpted physique. However, once having melded skurj essence into himself, his entire form now seethes with scarcely contained magma and ire. His eyes now hold a tortured rage and, courtesy of his bromance with Roger Covenant, he has one terrifying hand made of living fire and another that is frankly merely a puny human one. A bit of an embarrassment, really and in all events not a good look for any social occasion.