In the ninth century, a formidable Norwegian Viking named Kveldulf roamed the seas, unmatched in strength. He spent years plundering distant shores before settling down in wealth. Kveldulf fathered two sons, one of whom served King Harald Tangle Hair. Fearing the son's rising power, the king had him killed, prompting Kveldulf to seek vengeance. Alongside his surviving son and allies, he exacted retribution, slaying 50 men before fleeing to Iceland, where he perished en route. His son, Skallagrim, reached Iceland, prospered, and continued the family lineage.

Generations passed, and eventually, a descendant named Kari Stefansson was born in Reykjavik in 1949. Like his Viking ancestor, Stefansson grew into a towering figure, standing at 6’5”. He sought knowledge at the universities of Chicago and Harvard, but during the 1990s genetic revolution, he was drawn back to Iceland by the unique genetic heritage shared by himself and over 300,000 fellow Icelanders — a legacy from Kveldulf and the original settlers.

Stefansson envisioned an ambitious project: to compile a comprehensive DNA library of every living descendant of Iceland's early inhabitants. This repository, combined with Iceland's extensive genealogical records and medical history, would serve as a remarkable tool for uncovering the roots of human diseases and their cures.

In 1996, he founded Decode Genetics, propelling Iceland to the forefront of genetic research. “Our genetic heritage is a natural resource,” Stefansson proclaimed, likening it to the nation’s fisheries.

Embarking on this monumental task, he and his team collected DNA from 150,000 Icelanders, creating an extensive genealogical map. They successfully sequenced the entire 3 billion nucleotide genomes of more than 11,000 individuals, allowing them to infer the genetic makeup of the entire Icelandic population. They then searched for individuals missing specific DNA segments, correlating these gaps with health impacts, a journey that was only just beginning but already yielding significant findings.

By 2015, Stefansson's team identified rare mutations linked to increased risks of Alzheimer’s, gallstones, atrial fibrillation, and thyroid issues. Understanding how these mutations affected biological pathways could yield profound insights into some of humanity's gravest health challenges.

Historically, Icelanders documented the legendary tales of Kveldulf and other explorers in the Sagas of the Icelanders. Inspired by these narratives, I traveled to Iceland in winter to pen the story of a modern-day Icelander unraveling the genetic code.

December in Iceland is stark and cold, with the sun rising late and disappearing early. The winds sweep down from glacial peaks across the volcanic landscape. On a frigid morning, I set out from my hotel to meet Stefansson, bracing against the chill.

Decode's headquarters, bright and modern, resembles a warm refuge amid the harsh environment. Yet, I felt apprehensive, aware of Stefansson's notorious temperament. Due to a mix-up, I arrived half an hour late.

As I waited, Decode's press officer sat beside me, visibly agitated. He warned me that Stefansson's response could be unpredictable. “We’ll see,” he murmured.

At last, Stefansson appeared — tall, bearded, and dressed casually in a hoodie and sneakers. I offered my apologies.

“Americans can be arrogant, deceitful, and foolish,” he remarked with a smile, leading me into his office.

Stefansson often embraces a rebellious, Viking-like spirit, relishing the role of provocateur. The son of a renowned Icelandic journalist, he originally aspired to be a writer or poet, a dream that shifted unexpectedly one night when, after a night out with a friend, he ended up applying to medical school on a whim.

“I had no interest in it at first, but suddenly, I found myself in medical school,” he said, reflecting on his disinterest. “I found it incredibly dull. I’m not sure why I stayed.”

Yet, a personal tragedy motivated his medical path. His beloved older brother, a gifted athlete and his childhood hero, suffered a psychotic breakdown. The vividness of his brother's delusions, including a fabricated incident involving an ax, profoundly impacted Stefansson and his family.

“He was completely unhinged,” Stefansson recalled. “Schizophrenia alters your identity, changing how others perceive you.”

Driven by this experience, he delved into psychiatric literature, briefly considering a career in psychiatry. However, he found psychiatrists lacking in education and innovation, prompting a shift towards studying neurological diseases.

Since Skallagrim's time, Icelanders had lived in relative isolation, cultivating a remarkably homogenous gene pool. After completing his postdoctoral work at the University of Chicago, Stefansson's passion for science flourished, particularly in researching multiple sclerosis (MS), a debilitating condition where the immune system attacks the protective myelin sheath of nerves.

In the 1980s, alongside a graduate student, he painstakingly sought out proteins in the brain that might trigger such immune responses. However, the task proved frustratingly complex, leading him to consider genetics as a more viable avenue for investigation.

Realizing that every individual possesses approximately 20,000 genes, each comprised of millions of DNA pairs, he theorized that genetic variations could provide insights into diseases like MS. Misprints in genetic sequences, influenced by lifestyle, might be the underlying causes of many health issues.

Stefansson believed that identifying genetic differences among MS patients would likely reveal crucial links to the disease, making them promising targets for treatment.

In the 1980s, distinguishing these genetic differences was arduous, as demonstrated by his and Gulcher’s lengthy efforts to sequence a single strand of DNA. However, the advent of the Human Genome Project in the early 1990s heralded a transformative era.

Stefansson decided to conduct his MS research in Iceland, where the genetic homogeneity would simplify identifying disease-causing mutations, unlike in diverse populations like the U.S., where distinguishing specific variants is challenging.

He enlisted an Icelandic neurologist to recruit MS patients, encouraging them to bring healthy relatives for comparison. Many showed up with large family groups eager to assist.

While most geneticists relied on sibling pairs for studies, Stefansson recognized that distant relatives would offer more valuable insights due to their fewer shared genes. This approach would ultimately enable them to identify unique disease-causing mutations.

Confident in his method, Stefansson sought funding from the U.S. National Institutes of Health. However, reviewers questioned his reliance on Icelandic relatives without sufficient sibling pairs, highlighting their bias towards traditional genetic study protocols.

Undeterred, Stefansson envisioned a more ambitious project that would leverage Iceland's rich genealogical traditions, centralized medical records, and altruistic population. With a massive tissue bank and comprehensive cancer records, he believed that establishing an institute could unlock invaluable insights into human diseases far beyond MS.

Within months, he secured $12 million in venture capital, marking his return to Iceland to launch Decode.

One of his first actions was to access Iceland's largest genealogy database, containing 400,000 records. To enhance its completeness, Stefansson dispatched teams to review church records and census data.

As Icelandic leaders sought to bolster the biotech sector, Stefansson advocated for a comprehensive database integrating health records with genealogy and DNA samples. However, the proposal sparked controversy, facing criticism for perceived invasions of privacy.

Despite the backlash, the legislation passed, albeit with stringent privacy safeguards that ultimately led Stefansson to withdraw from the partnership with the government, fearing financial ruin.

Nonetheless, Decode continued its work, gathering medical records and DNA from volunteers, who filled out extensive questionnaires detailing various traits. By 2001, Decode reported significant findings linking genes to conditions like preeclampsia, osteoporosis, and Alzheimer’s.

With its initial public offering in 2000, Decode was valued at over $1 billion, leading to significant growth and expansion in the following years.

The Human Genome Project's draft sequence revealed that 99.9% of individual DNA bases are identical, suggesting that the key to common diseases lies within the remaining fraction. By identifying single nucleotide polymorphisms (SNPs), researchers could pinpoint genetic variations linked to diseases.

As the project progressed, scientists cataloged nearly 1.5 million SNPs associated with specific haplotypes. When Decode received its first SNP chips in 2006, Stefansson's team quickly identified genetic variants linked to atrial fibrillation, a serious heart condition.

However, skepticism about the new techniques began to surface. Critics pointed out that previous studies had failed to find significant genetic links to conditions like bipolar disorder, leading to discussions about the “mystery of missing heritability.”

Despite the doubts, Stefansson continued advocating for the value of common genetic variants in developing treatments. However, by early 2009, Decode faced significant financial challenges, eventually declaring bankruptcy in November.

Yet, Stefansson secured backing from previous investors, raising $40 million to revive Decode as new sequencing technologies emerged, promising rapid genome sequencing at lower costs.

With these advancements, Decode could identify rare mutations, potentially revealing significant insights into disease pathways. Stefansson emphasized that such mutations, often harmful, might provide crucial clues to understanding health conditions.

As Decode emerged from bankruptcy, excitement filled the offices. Stefansson and his team devised strategies to leverage whole-genome sequencing, allowing them to infer the genomes of over 100,000 Icelanders.

In 2011, the Decode team stumbled upon an intriguing discovery regarding a gene associated with Amyloid Precursor Protein (APP), known for its connection to Alzheimer’s. Surprisingly, individuals with certain mutations showed a reduced likelihood of developing the disease.

This unexpected finding led Stefansson to hypothesize that the mutation might also protect against cognitive decline. Testing this theory, they sequenced the genes of elderly individuals, confirming that those with the mutation exhibited no cognitive decline.

When Decode published its findings, it garnered significant attention, suggesting potential paths for Alzheimer's treatment.

The company continued to thrive, investigating links between paternal age and the prevalence of mutations associated with autism and schizophrenia. The results suggested a correlation between older fathers and increased mutation rates, drawing global interest.

In 2012, Decode caught the attention of Amgen, leading to an acquisition for $415 million. While some Icelanders criticized the profit motives, Stefansson remained committed to ethical responsibilities towards his compatriots.

By 2015, Decode had sequenced 2,635 Icelanders and inferred the genomes of over 100,000 individuals. Their groundbreaking work identified rare mutations linked to several diseases, paving the way for future research.

Stefansson concluded our conversation, reflecting on his journey in science. “If you can’t tell a story with your science, it’s not worth much,” he stated, emphasizing the significance of understanding DNA. “It’s the essence of life.”