The name Rayden is actually that of a deity known as the thundergod.
Rayden fighted with the earthlings against Shao Kahn.
He won and now prepares again for battle against the god Shinnok, who wants to take over everything. Rayden hid the amulet that gave god-powers to Shinnok, but Sub-Zero stole it and freed (without his knowing) Shinnok by giving the amulet to a wicked sorcerer.