Making Any Mob Aggressive

I am making a mob that summons minions, but since I can't really get the minions to attack their targets they aren't much help. I'm trying to get a neutral mob aggressive (Iron Golem), but I assume it would work with passive mobs too like a chicken. My question is how do you make a mob have an aggressive nature?

I also tried the Copy Combat Table for the minions, and that didn't work. I'm obviously doing something wrong.