The best-tasting Caesar will have minced anchovies ground into a paste.  Anchovies are an essential ingredient because they provide the right umami flavor.  It adds a briny, fishy, umami flavor profile or the savory element, which is so important.  We've also added Worcestershire sauce, which also has anchovies in it, for some extra umami. If you must substitute because you are vegan, use ground kelp instead of the anchovies.  This seaweed will still provide some of the fishy taste, and replace the Worcestershire sauce with the vegan version.