Mithology
The story behind the powerful hammer
The Gylfaginning
Thor is the foremost of them, he that is called Thor of the Æsir, or Öku-Thor; he is strongest of all the gods and men. He has his realm in the place called Thrúdvangar, and his hall is called Bilskirnir; in that hall are five hundred rooms and forty. That is the greatest house that men know of.
Thor has two he-goats, that are called Tooth-Gnasher and Tooth-Gritter, and a chariot wherein he drives, and the he-goats draw the chariot; therefore is he called Öku-Thor. He has also three things of great price: one is the hammer Mjöllnir, which the Rime-Giants and the Hill-Giants know, when it is raised on high; and that is no wonder, it has bruised many a skull among their fathers or their kinsmen. He has a second costly thing, best of all: the girdle of might; and when he clasps it about him, then the godlike strength within him is increased by half. Yet a third thing he has, in which there is much virtue: his iron gloves; he cannot do without them when he uses his hammer-shaft.
The Norse mithology narrative
This is how the god of storm and thunder Thor is introduces in the Norse mythology. The book we are talking about is the Gylfaginning, litterally "The Tricking of Gylfi". It is the first part of the Snorri Sturluson's Prose Edda after Prologue.
Snorri Sturluson is an icelandic historian and mythographer. In this book he proposed the hypothesis that mythological gods where human war leaders and kings. In their gravesite people used to gather to pray and honor them, and since their protection was invoked during wars or tribal hostilities, they began to be venerated, and that is how eventually they became gods.
Thor
Thor is a god then, son of Odin, the god's king, and Jörð, godness of the earth. Since he was the strongest within the Æsir dynasty he was living in Ásgard.
The iconography depicts Thor as redhead with a thick red beard and mighty muscles. As his father was considered the god's king he was more considered as the humans' god, and that is why the Vikings called themselves the "People of Thor".
His wife is Sif, godness of ferility, who gave him two sons, Þrúðr e Móði, while with the giantress Járnsaxa he had Magni.
In the traditional tales he is fighting and defeating a lot of powerful creatures, like the giants for example, and other monsters.
Thor is also known as a Marvel character, but there are few things that are reported differently.
Mjöllnir
But what is typical of his figure is the hammer Mjöllnir, the most powerful weapon. Mjöllnir was forged by the dwarfs Eitri e Brokkr, it roars like thunder every time it hits, emitting flashes when lashed at enemies.
In the sacred ceremonies reproductions of the hammer were used, for example during wddings, since the hammer was both symbol of life and death. In fact it was used in battle to kill enemies, but was also used to bring back to life.