Hmm. I'm not too familiar with cichlids, but I can give you a few tips for aggression in general.
~ How big is your tank? Most aggressive fish do better in larger tanks. They will usually pick one part (instead of the whole tank in smaller tanks) to claim as their territory. Other fish learn pretty soon about safe spots to swim in!
~ Lots and lots of plants/decor. Give the others a ton of places to hide and get away.
~ Rearrange the tank and introduce the most aggressive fish last. If he's in there before others, he'll think they're invaders he needs to teach a lesson to! Take everyone out and change the setup a bit and introduce him last. More than likely he'll reduce his aggression and see everyone more as part of his environment. If you do introduce fish after him, distract him with food while you're doing so.
Hope these work out