Leviathan was forged by the Huldra Brothers, Sindri and Brok, who also forged Mjölnir. After feeling responsible for the destruction brought about by Thor, Leviathan was made to oppose the power of Mjölnir. According to Sindri, the blade was infused with the echoing screams of twenty frost trolls (give or take) and it was made for and given to Laufey who passed it on to her husband Kratos before her death.

Approximate specifications are as follows: 

Weight: 30g
Length: (just axe, not including keychain): 10cm 
Material: Metal