Beorn often left his home, for hours or days at a time, for purposes not completely known. It is possible he could have left to drive out or eliminate enemies and other threats from the surrounding lands, and/or to find edible vegetation from further away. Beorn could be nocturnal as well, as he seemed to leave at night in bear-form. His origins lay in the distant past, and Gandalf the Grey suspected he and his people had originally come from the mountains.
Beorn named the Carrock and created the steps that led from its base to the flat top.
In The Hobbit, Beorn received Gandalf, Bilbo Baggins, and the thirteen Dwarves and aided them in their quest to reclaim the Dwarves' kingdom beneath Erebor, the Lonely Mountain. He was convinced of their trustworthiness after confirming their tale of encountering the Goblins of the Misty Mountains, and Gandalf's slaying of their leader, the Great Goblin.
Later, hearing of a vast host of Goblins on the move, Beorn arrived at the Lonely Mountain in time to strike the decisive blow in the Battle of Five Armies, slaying the new Goblin leader, Bolg, and his bodyguards; without direction, the Goblin army scattered and were easy pickings for the other armies of Men, Elves, Dwarves, and Eagles.
In the years between the Battle of Five Armies and the War of the Ring, Beorn became a leader of Men, including other shape-shifters, and woodsmen. His people were known as the Beornings, and they helped defend Thranduil's kingdom at northern Mirkwood. He died some time before the War of the Ring itself began, and was succeeded by his son Grimbeorn the Old.
In naming his character, Tolkien used beorn, the Old English word for "bear", which later came to mean "man" and "warrior" (with implications of "freeman" and "nobleman" in Anglo-Saxon society). It is related to the Scandinavian names Björn (Icelandic and Swedish) and Bjørn (Norwegian and Danish), meaning "bear". The word baron is indirectly related to beorn.