[Boromir88]

The connection to Beowulf is also compelling. Beowulf means, literally, "bee-wolf" which is (obviously) a poetic word for a bear.~Fordim

To expand upon your reference to Beowulf and 'bee-wolf.' The 'bee' connections go to explain the description of Beorn's pastures and 'huge bees' in The Hobbit:

'The drones were bigger than your thumb, a good deal, and the bands of yellow on their deep black bodies shone like fiery gold'~Queer Lodgings

If Tolkien used Beowulf as the template for Beorn, I could see the reasoning. Beowulf was human but a beserker warrior that posessed the strength of thirty men.~Beornings

That's a good connection to make with Beorn. The 'berserkergang' was a practice of the berserkers...or elite fighting Viking warriors. The meaning of berserker tends to vary from place to place, but the two common meanings were:

1) 'bare a sark' - referring to the berserkers fighting without any armor.

Or 2) Perhaps the one more applicable to Beorn - 'bear-shirt' - referring to berserkers who wore bear-skins, making the belief that berserkers would somehow turn into bears.

(Also, 'ulfhednar' means 'wolf-coats' which would be like the same sense in 'bear-shirt.' For an example Kveldulfr was described as a berserker in Egin's Saga who could change into a wolf.)

While Tolkien (to my knowledge) never actually uses the term 'berserker' anywhere in his books. It is important to note that Beorn's fighting at the Battle of Five Armies seems to be playing off the myths of 'the frenzy/fury' berserkers had and their invulnerability to weapons:

’Swiftly he returned and his wrath was redoubled, so that nothing could withstand him, and no weapon seemed to bite upon him."