Skadi is the dark goddess of winter, who is a warrior and huntress of fierce formidability who hails from the Jotun tribe, or race of giants, who have traditionally been enemies of the Asgardians, the latter of whom are themselves the product of a merging of two other tribes of deities, the Aesir and the Vanir. The giants, however, never made peace with either of the other two tribes. Skadi was the daughter of the giant Thiassi, who was killed by the Asgardian deities for kidnapping the goddess Idunn and thus temporarily depriving the deities of the fabled Golden Apples that confer longevity upon them, and which could only be harvested by Idunn. Following the murder of Thiassi, Skadi journeyed from the cold mountainous realm of Jotunheim, where the giants dwell, into Asgard, home of the Norse deities, to demand a wereguild--a form of compensation--for killing her father. Her request deemed valid under Asgardian law, she was invited to choose any of the bachelors amongst the gods for a husband, with just one stipulation: she could only choose by looking at their feet (don't ask me to explain the reasoning behind this stipulation). Hoping to pick the handsome god of light, Balder (who had not yet married Nanna), as her husband, she instead ending up inadvertently picking Njord, the god of the sea, who had the more attractive feet in her eyes. As a result of this union, Skadi became one of the few full-blooded members of the giant race to be accepted by the deities into their ranks (the other two being Loki and Saga).
The two attempted to love each other as best as they could considering the vast difference in their preference of environment--Skadi loved her home in the snow-covered mountains of Jotunheim, whereas Njord had an equally great love for his palace beneath the sea. The two initially reached an agreement to spend half the year living in each others' favored home, but during those times both found themselves longing for their preferred environs. As a result of this, the two ultimately decided to separate. According to some sources, it was Skadi who provided the poison used to torture Loki for being behind the machinations leading to the death of Balder.
Skadi can be a dangerous deity to call upon for aid, as her nature is quite dark and capricious, and though she is a formidable force to call upon when self-defense is required, she will tend to render this request with a degree of harshness, so those who call upon her should take this into consideration; her name is said to mean 'Harm' for very good reasons. Nevertheless, as a proud mistress of the wintery environment and a powerful warrior who wields both the sword and the bow and arrows with equal skill, she deserves respect for her important place in the order of things, for she personifies the extended hours of darkness and cold that comes with the season that people in some parts of the world (such as Scandinavia) look upon with dread. Areas of the world who experienced very harsh winters of extreme cold and a long length through the course of the year, with all the hardship that followed during those difficult months, tended to look upon the winter with a high degree of fear and negativity, and this was reflected in the nature of some of the deities associated with winter who were worshipped by people in those pre-industrial cultures (let us keep in mind that luxuries such as heated homes and electricity are all rather recent inventions). Skadi can also be called upon to aid her followers during the hunting season, particularly when they must do so in a cold and snowy environment.