Olajide Olayinka Williams "JJ" Olatunji (born 19 June 1993), known professionally as KSI, is an English YouTuber, rapper and boxer. He is a co-founder and member of the British YouTube group known as the Sidemen. He is the CEO of Misfits Boxing and the co-owner of Prime hydration drink, XIX Vodka and a restaurant chain known as Sides.

KSI registered his main YouTube account in 2009 and built a following posting gaming commentary videos of the FIFA video game series.