I was made aware of Iron Man and Captain America through watching the 1966 cartoons that were broadcasted up until the early 90's in my region.
(It really brings back memories)
Thor is the only major Marvel character that I wasn't familiar with up until the mid-2000s. I can't remember when I was first introduced to Hawkeye, but I've known about him since the 90's (probably as a guest character in a cartoon or comic). Black Widow, on the other hand, was a name I never heard of before the RDJ's movies. Overall, I don't think the Avengers as a team were that prominent or popular in many parts of the world before, and that's part of what makes the popularity of the movie so astounding, especially when you look at international numbers. I guess Marvel Studios played their cards right with their build-up to the release.