I don't think they are particularly aggressive. I used to have australorps, and that rooster would sometimes come after us with back turned, but my current roo doesn't, he keeps distance, and watches.
That said, he may be easter egger and not a true ameraucana. But everything I have read, he behaves just like that. He is warry, and good with protecting his flock, but he's not out for cuddles.
I also hatched a roo from his line and raised it for 2 months before rehoming, and he was the sweetest bird ever. Very talkative, also very attentive to his little flock. I thought he was acting like a shepherd herding all the silkie hatchlings around.
Pic of my roo uh, sorry, it linked the little guy, the rooster is few pictures in.