The First Men
Men who came east over a land bridge with bronze blades, cut down the forests, married the old gods, and became the North.
The fuller tale
They arrived out of Essos across the Arm of Dorne carrying bronze and leather and horses, and they made no secret of what they wanted, which was farmland. What followed was the longest war in the recorded history of the continent, and the strangest peace: having spent centuries killing the children of the forest, the First Men then adopted their gods wholesale and spent the next four thousand years praying to trees with faces carved by the people they had displaced.
The Age of Heroes belongs to them ÔÇö Bran the Builder, Lann the Clever, Garth Greenhand, Durran Godsgrief, the Grey King ÔÇö and so does every runic barrow and ringfort in the country. Every one of those names is doing far too much work in the histories to be one man, which is a maester's way of saying the record is songs.
South of the Neck the Andals broke them, married them and converted them until First Men blood was a thing a southron lord mentioned only in a boast. North of it they simply carried on. When Ned Stark says his people have held Winterfell for eight thousand years, he is claiming descent in an unbroken line from these men, and no one in the North thinks that is a boast at all.
The ground they held
What became of it ÔÇö if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.