I wouldn't say aggressive because it connotats a very bad attribute for their personality. I just think Slavic people overall usually are "less open" at first sight than people from other nationalities, like Spain, Italy or Latin America countries. It's a matter of culture, or cultural identity. Personally Russians use to be very nice to me, and a strong feature they have is that they are always willing to help when it comes to learning their language, at least many of them. 

Hi Jania.

I have heard that russian people are "cold", not agressive.

I've never met a russian.

Anyway, I don't believe in generalisations. :)

I went to graduate school with some Russian girls and this one Russian guy and they were very warm, friendly, open and like to drink! lol

There seems to be a stereotype of Russians that they like to drink alcohol and to get into fights, probably due to the alcohol.

Here in the USA, there has been a stereotype of people of Irish descent that is similar. I have Irish roots and I can say honestly that I have not touched alcohol in over 30 years. Also, getting into a fist fight is about the last thing that I would ever want to do.

So, yes, these kinds of stereotypes exist, but they are obviously false when you look primarily at the individual. A point that a Russian author who was very famous in the USA, Ayn Rand, was fond of making.