In his youth, Iofur killed a bear he met out on the ice, a great taboo among panserbjørne who are meant to accept a surrender in a fight. He later discovered that the other bear was his father, a fact he kept secret.
He later conspired with Marisa Coulter, pledging to keep Lord Asriel imprisoned on Svalbard in exchange for her aid. She gave him a drug which he used on a bear who quarrelled with Iorek Byrnison over a she-bear. The other bear became confused, and failed to show the proper signs of defeat in combat with Iorek, who lost his temper and killed his opponent. Iorek was then banished, leaving the way open for Iofur to become king.
Once in power, Iofur encouraged human practices among bears, such as wearing gold and silver ornaments, and had a palace of stone built for himself instead of the traditional panserbjørne ice fort. These changes were not popular, and even those who emulated their king in order to gain his favour seemed to feel uneasy about it.
Raknison's reign eventually came to an end when Lyra Silvertongue (or Belacqua as she was then known) crash-landed in Svalbard and was brought into the king's dungeon. The girl talked her way into an audience with Iofur and, aware of his obsession, convinced him she was Iorek's dæmon, claiming Iofur could take her for himself if he defeated Iorek in single combat. Iofur was convinced by her knowledge of his secrets (gleaned via the alethiometer), and allowed Iorek to enter Svalbard. Lyra explained her ruse to Iorek, who realised his opponent was vulnerable to tricks. Thus, despite Iofur's physical advantage and his own exhaustion, Iorek won the duel by feigning weakness and causing Iofur to expose himself. Iofur died in the duel, and his imposed human traditions were gladly abandoned by the panserbjørne when Iorek became king.
Iofur Raknison was large and powerful, even for a panserbjørn, but the thing that truly set him apart was that he thought like a human. Unlike other bears he kept secrets, used deceit and sought power, but more than this he wished to have his own dæmon and be baptized, making himself truly equal to the humans he emulated. This obsession led him to carry a human-shaped doll as a surrogate dæmon, his logic seemingly being that since humans have animal-shaped dæmons, bears would have human-shaped ones.
Iofur's human-like behaviour dampened some aspects of his bear nature, most notably his ability to see through trickery. This proved his undoing when he was tricked by both Lyra Silvertongue and Iorek Byrnison.