Admiral Kolifnn is the ruler of Ondalina, the father of Ragnar Kolfinsson and Astrid Kolfinnsdottir, one of the Six Chosen Mermaids the Iele summoned.
Kolfinn's daughter Astrid loses her singing voice shortly after celebrating Månenhonnør. Kolfinn summoned the best doctors in order to cure his daughter, but they are unable to solve even the mystery of why she lost her singing voice. As result, Kolfinn is forced to break the Permutavi, in which Ondalinian and Miromaran children of the ruling dynasties are exchanged in order to improve relations, as Ondalinians did not believe in revealing weaknesses like Astrid's inability to songcast. Astrid's condition was kept from all but a few trusted family members and members of the military.
When Astrid wandered too close to a mother polar bear and her cubs, she had been unable to songcast to defend herself. Kolfinn instead comes to her rescue, driving the animal off, and getting scarred in the process. He did not kill her as the mother polar bear was only defending her young, as he had. Afterwards, he scooped up a sobbing Astrid and gives her advice on what to do when confronted by a polar bear.
Admiral Kolfinn is the ruler of Ondalina. He was suspected by many Miromarans, and Matalins in Deep Blue and Rogue Wave of attacking Miromara and killing members of the royal families. However, this was not true, as Astrid pointed out, her father was too honourable to do such repulsive things, and would not risk his sister Sigurlin's safety, as she lives in Tsarno, Miromara with her family. In the end of Deep Blue, Kolfinn is revealed to have had an attempted assasination when a sea burr from Miromara is placed under the saddle of his hippokamp. Then venom from the Medusa Anemone, also from Miromara, is placed in his food. It slowly killed him. In Dark Tide, it is revealed that the culprit was in fact, Portia Volnero and that she enlisted the help of Rylka, his commodora, or Second-in-Command, to assassinate him and blame Ondalina for what happened to Miromara, Isabella and the Matalin royals.
In Dark Tide, Astrid returns from the Iele to discover that Kolfinn was not recovering as she had thought, but is instead, dying. Kolfinn sees the Bloodsongs that show that Bilaal and Isabella were in fact, murdered by Isabella's own brother Vallerio, who framed Kolfinn and Ondalina for the murders and invasions. He learns about Abbadon, but refuses to let Astrid go as he fears for her safety and believes that a monster that might be freed is not so grave a threat as imminent war. As Ragnar, his son, is young, he orders, once he dies, that Rylka and he jointly rule and Astrid marry Tauno, Rylka's son, as Ragnar has not married or had any sons, and therefore Astrid is next-in-line, but is unable to songcast, so Kolfinn feeling that no merman would risk marrying her for fear that resulting children would be unable to songcast, or that Ragnar's power would be called into question as well, insists that Astrid marry Tauno. Kolfinn is killed when Astrid discovers the real poisoner and traitor, Rylka. Rylka added the final dose of poison, supplied by Portia Volnero to prevent anyone from finding out who had been behind this.
Kolfinn is said to have long, thick hair the colour of a winter's sun, riveting ice-blue eyes he has thickly-muscled arms, covered in tattoos, a sign of his rank and achievements, and an orca's tail. However, when he becomes ill, his powerful body becomes wasted, his now-sallow skin stretched over his skull, and his hair became stringy and dull.