Is Coulson dead or not?

This is a silly question, we know, but it should be answered: Why are the Avengers so unaware of the existence of Agent Coulson?

As we’ve said before, Coulson was one of the characters who appeared in more than one movie up until the release of the Avengers, effectively introducing SHIELD to the audiences. He became a fan-favorite – but this didn’t stop Joss Whedon, who killed him in a most satisfying way (if we can call it that): His death was the one that united the Avengers, and convinced them to battle Loki, instead of one another.

Apparently, Coulson was a pretty important friend (or something) to all of the heroes (we know for certain that he was closer to Iron Man, because of his friendship with Pepper Potts). So how come none of the Avengers is aware of his existence? How come he isn’t mentioned in the big MCU movies, despite his being alive and despite his being so important?

This is one of the questions which will never be addressed in the MCU, simply because his revival had nothing to do with the internal logic of the shared universe. It was just a move to cash in on the Coulson fan base.