The Inuit themselves could have told you this, as they have stories about people they called the Tuniit. The Tuniit were bigger and stronger than them, giant men supposedly able to crush the neck of a walrus and drag it home like it was just another trip to Safeway. Other stories say the Tuniit knew magic and slept with their legs in the air so the blood would drain from their feet, making them light enough to outrun caribou (we tried it ourselves, to mixed results). But despite their all-around badassery, the Tuniit were a shy people who tended to keep to themselves and avoid conflict. They were "easily put to flight" if needed, so the Inuit took many of their best hunting grounds, while the Tuniit receded and vanished.
These stories were long considered myths, what with the magic and caribou-tackling and not super-swell relationship between Native Americans and the general scientific community. But a 2014 genetic study confirmed that while the Tuniit may not have bench-pressed seals, they did exist as a distinct people. Dubbed the Dorset, they lived in the Arctic for over 4,000 years, but vanished by 1300 CE, just 300 years after the Inuit arrived.
Their most distinct feature was their relative lack of genetic diversity. Not only did they migrate to the Arctic with few women in their group, but they also steadfastly refused to bone down with the Inuit and any other cultures they encountered. And that's a notable aberration, because throughout the epic sweep of history, discovering what a new culture was like in bed was inevitably a top priority after first contact.
While it's unclear where the Dorset migrated from, their very existence shows that people arrived in North America in more ways than previously believed. And given that the Inuit of their time were just as baffled by the Dorset as we are today, they're another valuable reminder that the pre-European history of North America is far more complicated than "A bunch of Natives just hung out for a while." In addition to being a society of wallflowers, the Dorset apparently preferred to hunt with spears despite bows being far safer, and their surviving carvings imply a focus on rituals and spiritual beliefs that may explain why they chose not to intermingle. As for what happened to them, the best guess anyone has is that diseases brought over by Viking traders did them in. Way to go, Vikings.