Complex sentence: As a music video director, his most notable and frequent collaborator is Rihanna, the two have worked on sixteen music videos together throughout her career, beginning with "Unfaithful" in 2006 and most recently "Diamonds" in 2012.
Split into simpler sentences: As a music video director, his most notable and frequent collaborator is Rihanna. The two have worked on sixteen music videos together throughout her career, beginning with "Unfaithful" in 2006 and most recently "Diamonds" in 2012.