Tyr, represented by the spear shaped runic letter  and known as Tiw by the Anglo-Saxons, is the god of law and order commemorated in the day name Tuesday. (The Roman war god Mars is equivalent to Tyr in many ways, and so recalled in the modern Italian name for Tuesday, 'martedi'.) 

Fenrir ranged freely about Asgard, the land of the gods, and had special status despite his fearsomeness. Such was his courage that only Tyr was willing to feed this beast. Wearying of the treat of wolfish violence, Odin (Woden to the Anglo-Saxons) commissioned dwarfs to forge from magical materials a fetter with which Fenrir could be bound. Only dwarfs could have wrought anything so cunningly, for it was made from the breath of a fish, the sinews of a bear, the spittle from a bird, the hairs of a women's beard, the roots of a mountain, and the noise made by cat as it walks. The resultant fetter was as light as a silken cord and yet completely unbreakable. Wily Fenrir refused to accept such an innocent looking thing about his neck without some form of surety: he demanded that one of the gods place his hand into the wolf's mouth. Only unflinching Tyr agreed to do so. When an enraged Fenrir realised all his mighty strength could not break the slender cord, he extracted from Tyr his payment - the huge jaws snapped shut and Tyr lost his hand.