There definitely cool and develop personalities. I started with two in a 29 gallon but like highlander, "There can be only one." He never messed with any of the fish at all and will crawl into my hand and hang out. Right now though he is riding solo.
I got one recently in a 12g all to himself, always wandering about and when I get close to the tank it runs over to the glass and waves its claws at me trying to look intimidating haha.