i would say my clown when i added a pair of them the female chased all the other fish for about 3 days and pushed the male around also. but she chilled out now, just a show of dominance. also my kole and alge blenny battle it out a bit over food.
Right now, since my tank is still fairly new, my cleaner shrimp. His highlight of the day is to be hand-fed and then clean my fingers.....pretty amazing critter.
That would have to be my Emperor Angel. Still just a juvenile, he's definately "da man"! The last fish added about six months ago, didn't take him long to become head of the household over kole tang,2 perculas,2 green chromis.