The biggest mystery that was ignited by the "Agents of SHIELD" TV series was Agent Phil Coulson being alive.

Millions saw him getting blasted by Loki in "The Avengers" and his death was even a rallying point used by Nick Fury to form a bond between the conflicting Super Heroes.

If he survived the blast, then Nick Fury was lying and it's pretty certain that the Thor, Iron Man, Captain America and the Hulk (definitely not the Hulk) would appreciate getting duped, since Phil Coulson, in many different ways, has a n attachment to them.

Therefore, it's safe to say that he actually died.

So why is he driving around groovy cars in "Agents of SHIELD?"

The show gives very little clues that actually opens to much speculation. However, beyond the series, there are some hints that can be found in the most unlikely places.

Clark Gregg drops some hints in an interview with Larry King (because it's the one and only Larry King):

 "What's the deal with Tahiti. Tahiti's a magical place. I keep saying that... it's where I went to recover after being impaled and as I say in the pilot, it was a spectacular experience, I had a beautiful physical therapist and I read Travis McGee novels all day. But every time someone mentions it lately I seem to go into post traumatic stress so I think there's a little more to Tahiti than meets the eye. There's a much darker, more interesting story there. Something much more magical has gone on to bring this guy back to life."

Is "Tahiti" the literal island Tahiti? Or is it a reference, a code name to a different place? Is it a physical place or an entirely new plane of existence (this is the Marvel Universe after all)?

If it's magic, then who did it? Two suspects: The Scarlet Witch (who is confirmed to join The Avengers sequel) or Dr. Strange (who has actors like Johnny Depp, being attached to the role when the movie is still being conceptualized).