Rajinikanth did not appear in the previous Expendables films because he had more important things to do, like saving the world.
This actor has been a phenomenon in southern India for decades and became more widely known only after the advent of the Internet.
He has massive pop culture appeal that admittedly began as a rip-off of Chuck Norris jokes, but it grew to become an Internet meme of its own.
What role could Rajini play in the Expendables crew? Why, any of them, of course!
He is a certified Ubermensch and an all-round badass. His mere presence might be enough to send the baddies running in the opposite direction hoping they were never born.