The name has its origins in propaganda from the established party that the rebels were so poor that they made their shoes of birch bark.
Today, the Birkebeins are popularly celebrated for having escorted the one-year-old Haakon Haakonsson, an heir to the Norwegian throne, safely from Lillehammer to Østerdalen to Trondheim, a long and perilous journey through treacherous mountains and forests.
It was this lawless population that became the foremost basis of the Birkebeiner, even though it is questionable whether their leaders were paupers wearing shoes made of birch bark.
The powerful Trønder families were simply being left behind by their peers in the south, who had acquired a strong leader in the Vestland earl Erling Skakke in the mid-12th century.
In the early 1160s, Erling had taken control of Viken and the bishopric of Nidaros and had subsequently made his underage son Magnus Erlingsson the king of Norway.
After some initial victories for the Viken party, the tables turned when Sverre entered the political scene claiming to be the illegitimate son of king Sigurd Munn.
The Birkebeiner's political program was a continuation of earl Erling's centralization which underscores the geographical motivations behind the movement.
In 1206, the Birkebeiners set off on a dangerous journey through treacherous mountains and forests, taking the now one-year-old Haakon Haakonsson to safety in Trondheim.
Bagler pretender Philip Simonsson was recognized as ruler of the eastern third of the country, Østlandet, without the title of king.
The mascots Håkon and Kristin of the 1994 Winter Olympics are depicted as Birkebeiner children, bearing the names of the son and daughter of king Sverre.