I reality I don't think many people occupy one role in their circle of friends - if they even have a circle. Most people I know have a friend or friends which occupy different parts of their lives and these friends may rarely come into contact with each other.
For me I have some old friends from high school, friends from uni, friends I've met out and about etc. some of these are people I talk to often and some not.
Some friends I may not speak to for weeks but I know they are there if I need anything and viva versa. Then there are the friends you might see every week or so to go out partying with but it's not a deep relationship.
And just like how each of these play a different role in my life, I play a different role in theirs.
To some I'm the jokey fun party person. To others I'm the grab a coffee and catch up and talk about the news with. To others I'm their shoulder to lean on etc etc.