The 13 'Santa' brothers who usher in Christmas in Iceland are supposed to have descended from trolls and ogres who love to terrify young children.
Tradition holds they visit homes, in succession, on the 13 days before December 25, depositing either sweets or a toy or -- the worst case scenario for bad behaviour -- a potato in shoes children have left by a window.
"The Santas are trolls and come from Icelandic folklore; it is in their nature to be evil," explained folklorist Steinunn Gudmundardottir.
Known as Yule Lads, they can strike fear in the hearts of youngsters, as witnessed when "Stekkjastaur", the first-born of these 13 troll "brothers", made an appearance at Iceland's National Museum 13 days before Christmas.
About 100 children waited anxiously as he burst into a room, sporting a traditional Icelandic wool sweater, knickerbockers and a bright red wool cap that matched his rosy nose and cheeks half-hidden by a bushy grey beard.
"I am not only the first Santa to come to town, I am also the eldest," he bellowed, stomping sternly and demanding who knew where his name came from.
A few trembling hands went up before bolder children shouted: "because you are inflexible" and "because you drink sheep's milk". Both were right -- all 13 "Lads" have their own distinct traits and Stekkjastaur, which translates to "Sheep-pen Clod", likes sneaking into sheep pens to suckle the yews but does so clumsily because he has stiff knees, according to Icelandic folklore.
Over the centuries the Yule Lads "slowly evolved into being kinder, although they occasionally tease and maybe steal," Gudmundardottir told AFP.
She said the change probably dates back to a 1746 law banning parents from scaring their children with the likes of evil trolls and Santas.
"The gift-giving came later, in the 20th century, and this had to do with influence from the American Santa Claus," she added.
"I remember the first time I got a potato in my shoe," says Margret Yr Ingimarsdottir, a 25-year-old student and mother.
She was six and tried to be brave, "but in the evening I broke down and cried, terribly upset that Santa had thought I misbehaved and only deserved a potato instead of a nice toy or candy."
The trauma would not keep her from doing the same to her own children.
"My daughter is only two years old now so I wouldn't put a potato in her show, but when she gets older, and if she misbehaves, I wouldn't think twice about it," she said.
While the 13 brother Santas have gone through a mellowing process, their mythical parents Gryla and Leppaludi are known as the most hideous and mean-spirited ogres ever in Iceland, and quite possibly the world.
Stekkjastaur insisted, in his museum appearance, however, that his mother too has improved over time.
"It now only happens on rare occasions that Gryla stuffs misbehaving children into her pot. We try to keep her in check," the first Yule Lad said.
"Sadly, making sure she doesn't cook kids doesn't change the fact that she is a terrible cook," he laughed.
And although the Icelandic Santas themselves are less evil than in the past, they still enjoy a good tease.
Stekkjastaur warned, at the museum, that his "brother Hurdaskellir, or Door Slammer, who is the seventh to come to town, is a bit of a bully. "All the door slamming can frighten the little children sometimes," he said.
According to Gudmundardottir, it is no coincidence this elaborate mythology surrounding Christmas surfaced in Iceland.
"With little daylight and no electricity up in the mountains where many people lived, it is not surprising that stories were spun from figures that came from the darkness," she said.
"People were very connected to nature, and it seems only reasonable that they imagined that there was something else living among them in the shadows."
And with its almost other-worldly nature, its volcanos and geysers, Iceland does not appear to be the most natural setting for one saintly old gentleman in a flashy red suit.
The US-style Santa Claus, whom popular legend now holds is a cousin of the Icelandic Yule Lads, "gave us all a red suit like his to wear," Stekkjastaur told the children at the museum.
"We sometimes put it on when we go to Christmas balls and such," he said but, reverting to Icelandic folklore, added: "on our walk from the mountains and to town it is best to stick to our traditional clothing."