(also Tir, Tiv, Tiw, Tiwaz)
Tyr was the god of war, an Aesir. He was the son of Odin and Frigg.
When the monstrous wolf Fenrir became very powerful, the gods decided to imprison the beast. No ordinary chain could restrain Fenrir, so Tyr had to put his hand in the mouth of the wolf as a sign of goodwill while the other gods created a magical restraint. When Fenrir realized that he had been tricked, and that he could not free himself, he bit off Tyr's hand.
Tyr fought at Ragnarok, where he was destined to battle with Garm, the watchdog of the underworld - a fight which would result in both of their deaths.
The name Tiw, which he was called by the Anglo-Saxons gave rise to the name Tiwesdaeg, or Tuesday.