1) One of the greatest men to every walk the earth.
2) Utmost respected by not only the Catholic Religion but others including Judaism and Islam.
3) Considered by many to be the greatest man alive until his death on April 2, 2005.
4) Earned the respect of billions of the world's population.
This is a greeting meant to say what's up, what's crackin', or another such colloquial greeting. The reason it is popular is because Poppin' Fresh is the Pillsbury Doughboy's former name (the name was changed to update little Freshy's character and bring him into modern times). The phrase is not questioning what Poppin' Fresh is, rather it is using poppin' in it's slang meaning, and it is using fresh as a noun, not an adjective. Fresh refers to the person being addressed by the question.
Bob: Yo
Joe: Yo, what's poppin' fresh?
Bob: Not much kid, what's crackalackin'
A dude who's an athlete, hot and everyone thinks he actually gets lots of pussy, but he's actually chill, kinda shy, likes music, introverted, super smart, kind of a nerd and wants to meet someone he vibes with.
Michael: Yo Marshall hot. He must get lots of pussy Derek: Nah, he's a Popular Loner