Jormangandr
Jormangandr is the son of Loki and the Jotun Angrbodr who resides in the Ironwood on Migard, and the brother of Fenrir, and Hel.
He is so large that he encircled the entire oceans of Midgard, creating the tides and the waves.
Jormangandr is Slain by Thor during Ragnarok, but also kills Thor at the same time.