Thor also known as T-Money is the Nordic god of thunder and the older brother of Loki as well as the paternal uncle of Taylor Evermore. Thor is a prominently mentioned god throughout the recorded history of Germanic and Scandinavian peoples. He was the son of the Allfather Odin, King of the Gods.
In Nordic mythology, Thor was the companion of his own realm of Asgard and protector to the realm of Midgard (Earth) and came to the aid of the humans whenever he was needed.
In the show, when Lokiinvaded Orchid Bay City, Juniper Lee summoned him to help combat the evil god and save the world from being consumed by darkness. After he returns his brother to banishment, and restores the magical balance, he gives June his card and tells her that if she ever needs anything to just give him a call. Thor returns in season three when he pursues a Vindolf Hobgoblin to her school which it is hiding in. If the Vindolf Hobgoblin isn't found as soon as possible, Thor will destroy the school to take out the monster.
Mjölnir is depicted in Norse mythology as one of the most fearsome weapons, capable of leveling mountains, can blast devastating lightning projectiles, and create storms and hurricanes. When thrown Mjölnir will always return to Thor's hand. The hammer was made by the dwarven brothers, and was constructed from the core of a dying star.
The Mjölnir in the show is used by Thor to summon lightning, the Trellekian Trolls needed for Loki's banishment and for huge displays of power. It seems heavy enough to do some real damage when he intends to use it to destroy Orchid Bay Middle School but as shown by June, it is possible to stop it with Te Xuan Ze strength.
In the show, Thor is given an introductory entrance as would be normal in other media, then immediately depicted as a laid-back "surfer dude" who enjoys spending time at limbo parties, which contrasts him greatly with Loki, who does not enjoy parties with other people at all.
Thor gives Loki two options for redemption out of banishment: either limbo or being bound to a cliff while poisonous snakes feast on his entrails. The first is a reference to what the Loki of actual Scandinavian lore was punished with.
Thor and Loki have a sibling animosity between the two, but when Thor plays limbo during the credits, Loki seems to be cheering him on as well and quite cheerfully at that.