OG Juan, whattup?
I'm a little upset that you wasn't involved in this whole process
But it's all good

from Jay Z – My 1st Song Lyrics on Rap Genius

Meaning

Juan “O.G.” Perez, later famously shouted out in “Empire State of Mind”. He is pictured below with Jay and Lebron James

He was the owner of Baseline Studios where Jay worked out of, but apparently he wasn’t involved in The Black Album

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