He's the son of Odinn and Jord, the personification of primitive, unpopulated Earth. Through Odinn, he has numerous brothers, most notable of whom are Baldr, Bragi, and Heimdallr.
Consorts & Children:
He's the husband of fertility goddess Sif though has a giantess named Jarnsaxa for a mistress. He fathered Modi, the god of battle wrath, and Magni, who's considered the god of might as well as the only one of the gods stronger than his father. In fact, Magni is the only one other than Thor able to lift the infamous hammer Mjollnir.
Notable Stories Involving Him:
Thor is often depicted as a large, muscular man with red hair and a red beard, who sometimes can be seen riding a chariot pulled by two goats. He's seen as a protector of both the gods and humans, and it's from his name that we get Thursday. His greatest nemesis is Jormungandr, a sea serpent who encircles Midgard (Earth); in fact, it's said that when Ragnarok (the end of the world) arrives, he and the serpent will kill each other.
He often carries the hammer Mjollnir (meaning 'lightning' because that's what happens when he throws it), which can be used to either destroy his enemies or consecrate places and unions. He'll also sometimes be seen wearing a belt which can double his strength, making him even more formidable.
Thor Around the World:
Due to his association with the sky and weather, the Romans identified Thor with their Jupiter, though he's also been associated with Hercules due to his strength.
SOURCES: Wikipedia, Encyclopedia Mythica, & The Ultimate Online Resource for Norse Mythology and Religion