At up to 24 feet long, the Greenland shark is the largest fish in the Arctic. It used to be thought that it spent all its life in the cold water, but recently it has been discovered that these are the only waters where it comes to the surface, as they are the only waters with a cold enough surface temperature. But the Greenland shark could be common all over the Northern hemisphere in the deeper waters. There's probably one behind you right now.*
Also don't try and eat them. Their flesh is poisonous because it contains a weirdly high level of urea, because they don't have any kidneys. Icelandic people get round this by burying them in the ground for a couple of years until all the urea has decomposed, but apparently this is quite the acquired taste.
*If you are in the deep waters of the northern hemisphere.