They are like any other medium/large cichlid. They each have their own temperament and personality. No two fish are the same. No one can generalise their temperament, they can only give you their experiences.
My experience was that my 6.5" male was a pussy cat until fish started on him, then he went medievil on them but went straight back into pussycat mode. He took 2 bite size Uaru under his wing and protected them. He basically raised them, they were the only fish in the tank that could steal bloodworm and pellets from his mouth without being chased. He really took a shine to them.
My next male was a bit different. I put him in at about 2" and when he was about 3.5-4" he began to start fights with my female midas who was a thick 9" at the time but luckily for him very gentle and reluctant to fight. He was a prick of the highest calibre. He had to go or he would have been killed, ballsy but very stupid.
They can get to 12" sometimes a bit more but usually less for males, females hit about 6-8" and contrary to popular rumour they do not stop growing when they lay eggs. They just slow down a lot, if they stopped growing many people would have midget GT's as some begin laying at quite small sizes.