Nina Williams (ニーナ・ウィリアムズ Nīna Wiriamuzu?) is a cold-blooded Irish assassin that made her first appearance in the original Tekken game and has appeared in every Tekken game since. Nina has a lethal fighting style, consisting of throws, grapples, and holds. She has an infamous rivalry with her younger sister, Anna Williams.

During the end of Tekken 2, both Nina and Anna undergo Cryogenic Sleep. They are experimented upon for 15 years (this is the reason why they both remain physically young throughout the tournaments). While in cryogenic sleep ("cryosleep" for short), her ovum was taken without her consent and was used to create Steve Fox (who first appears in Tekken 4 and onwards).