It's really not that hard to tell actors from their characters
Like, this is Loki
And this is Tom. They have different colored hair.
This is Castiel
And this is Misha. They wear different clothes.
This is Tony Stark
And this is Robert Downey Jr. They have different names.
Simple
Actually, don’t forget that Tony Stark is about half a foot taller. RDJ is a tiny tiny man and it’s hilarious.