While the recent history of Christmas beers is rather marketing-driven, both in the US and around the world, the tradition of brewing special beers for this time of year draws on a number of deeper traditions.
The Scandinavian countries have, perhaps, the strongest claim in this regard. The Vikings enjoyed a strong, malty beer during their Jul—or Yule—celebrations: their December 21st festivities involved them 'drinking Jul,' with drafts offered up to Odin, Frey and the other Norse gods.
In fact, even after Christianity became the official religion, brewing Christmas beer was enshrined in law: Norway's King Haakon I ('The Good', c. 920-961) decreed that each household must brew a measure of beer for Jul, now moved several days and rolled into Christmas. The tradition was further reinforced by the Gulathing Laws, written down in the 13th century (though probably established long before), which not only required each peasant household to brew a Christmas beer and hold something of a party, but it outlined specific penalties for failing to do so—fines and a loss of property were possibilities for those shirking their brewing responsibilities.
Sweden and Denmark, with their shared Viking beginnings, were equally enthusiastic about their holiday brewing and drinking, both from that early period until recent times—indeed, the Swedes were among the first Europeans to bring a Christmas beer tradition to North America in the 17th century.
Commercial production of Scandinavian Christmas beers only began in earnest in the late 19th and early 20th centuries, but the story continues today; modern Scandianvian brewers, even those that produce little beyond fairly generic lagers the rest of the year, continue to brew Julebryg and Juleøl for Christmas—or for a Jul revival.
The Scandinavian Christmas brewing phenomenon did not go unnoticed elsewhere; in 1804, an anonymous British correspondent noted Scandinavian holiday brewing traditions as outside the wider European norm: the Christmas beer, which had been brewed in October, was 'pleasing to the palate, but heady.'
Of course, strong holiday beer was not actually new to Britain—it had been memorialized in song by 1681. 'The Merry Boys of Christmas; Or, The Milk-Maid's New Year's Gift' celebrated having a strong Christmas beer (or several)—and special Christmas beers were not unknown to 19th century commercial brewers in Britain.
Though there are many modern Belgian Christmas beers, one of the country's most famous exports, Stella Artois, has lost much of its original seasonal luster. While modern marketing positions the now-ubiquitous lager as coming from a brewery with medieval origins, Stella itself only appeared in 1926, launched as a Christmas beer and named as a nod to the storied Christmas star (the 'Artois' was courtesy of 18th century brewer Sebastianus Artois, who took over Den Horen Brewery in Leuven, Belgium, in 1708). Indeed, more recently that heritage is being played up again, with the release of a Christmas album tie-in, but the pale, golden lager does not, on the whole, match the current stereotype of a dark, malty Christmas beer.
Conversely, a British beer that has become a Christmas tradition began life as something altogether rather different: Young's Winter Warmer was originally a Burton ale, which was much stronger and sweeter than its modern counterpart. While the rise and disappearance of the Burton style is a much longer story, by more recent times, it was often more popular during the winter—not surprisingly, given its strength and 'warming' abilities—so it is not so unusual that it has largely morphed into a Christmas beer—at least for the time being.
Perhaps the most famous modern Christmas beer is Samichlaus, which began life in Zurich in 1980. Its birth is a reminder of how far beer has come in the past thirty-odd years, not just in terms of variety, but from a scientific perspective.
The beer, named after the local version of Santa Claus, was once the strongest lager in the world; it's 14(ish)% ABV was only possible because the Hürlimann brewery had developed yeasts capable of surviving at such high gravity—something that seems almost commonplace (although still technically difficult) in today's brewing scene. The beer disappeared after the 1996 vintage, but returned in 2000, with a move to the Eggenberg brewery in Austria. They continue to brew the beer once a year, on December 6th, and they maintain the original method of aging the beer for nearly a year before bottling for its Christmas release.
So when you enjoy a Christmas beer this year, think back to some of those that came before it —or go 'full Viking' and make your own!