Hybrid, usually a trimac x midas/red devil. They can get pretty big, 14-15 inches or so. Aggression depends on the individual fish, but they have the potential to be up there.
Generally considered to be amongst the most aggressive cichlids out there...if you were to put one in the tank I see in your signature, I would bet money on it being the only fish left alive after a week.
Most of the ones I've seen are really aggressive. Fasting them makes them bolder. The big ones will draw blood if they attack your hand. They have great characters actually. Most of them have this characteristic of centering their attack on the eye of another fish. Usually best if kept alone in a tank. It would beat up or kill its companions quite easily. I agree with Toirtis.
One of my LFS usually has around 20 flowerhorns on sale. They keep each one in an individual tank completely alone, even the 3" ones - I'm guessing they do that for a reason.
All the flowerhorns I've ever seen have been extremely aggressive. I had one some time back in a 55gal growout tank with a beani hybrid and motoguense - all around 6 inches, and the flowerhorn had to be seperated. If I walked anywhere near the tank, it would put the other fish down in case I was feeding them. It wanted all the food to itself, and it was getting it.