In Norse mythology

Norse mythology

Norse mythology, a subset of Germanic mythology, is the overall term for the myths, legends and beliefs about supernatural beings of Norse pagans. It flourished prior to the Christianization of Scandinavia, during the Early Middle Ages, and passed into Nordic folklore, with some aspects surviving...

, Hildisvíni (“battle swine”) is Freyja's boar

Boar

Wild boar, also wild pig, is a species of the pig genus Sus, part of the biological family Suidae. The species includes many subspecies. It is the wild ancestor of the domestic pig, an animal with which it freely hybridises...

 which she rides when not using her cat-drawn chariot

Chariot

The chariot is a type of horse carriage used in both peace and war as the chief vehicle of many ancient peoples. Ox carts, proto-chariots, were built by the Proto-Indo-Europeans and also built in Mesopotamia as early as 3000 BC. The original horse chariot was a fast, light, open, two wheeled...

.

It is also said to be Freyja's human lover, Ottar, in disguise, and is the reason why Loki consistently accuses her of being "wanton" by riding her lover in public.

It was also the helmet of Áli

Onela

Onela was according to Beowulf a Swedish king, the son of Ongentheow and the brother of Ohthere. He usurped the Swedish throne, but was killed by his nephew Eadgils, who won by hiring foreign assistance....

 that was taken by the Swedish king Adils after the Battle on the Ice of Lake Vänern that ended with Áli's death.

In Beowulf

Beowulf

Beowulf , but modern scholars agree in naming it after the hero whose life is its subject." of an Old English heroic epic poem consisting of 3182 alliterative long lines, set in Scandinavia, commonly cited as one of the most important works of Anglo-Saxon literature.It survives in a single...

, it is said that a boar on the helmet was there to guard the life of the warrior wearing it.