Khalid Azar was the buyer during Charles Renard's weapons deal at Rendard's museum.
While the deal is being struck, Azar sent an assassin to take out Renard's men. Bourne kills the buyer's assassin and makes it to the site of the weapons deal. He tries to find the weapon, but Renard and Khalid get to it first (the weapon is revealed to be a dirty bomb), and then Azar double crosses and shoots Renard. Bourne changes his primary objective to killing Azar. In the crossfire between Azar's and Renard's men, he manages to chase Azar through the museum and shoot down his helicopter.