Most cichlids are aggressive. Are discus?
Absolutely, uncontroversially, NO!!! Discus are probably the most docile and easily bossed-around cichlid you will ever see. The only time that discus are aggressive is when they’re breeding. Otherwise they’re sheep. This is one of the reasons that tankmates for discus should be chosen with great discretion. And vise versa, discus should not be added to an aquarium with fish known for being territorial or aggressive.