I'm the son/sun of the South Pole plus Alaska's dad
Got niggas like "DAG!!", flow is like crazy gone mad

from Lupe Fiasco – Thank You Lyrics on Rap Genius

Meaning

Metaphor to interpret how cold his rhymes are.
Dag is just another term for “damn"
His flow is crazy gone mad means it’s just fuckin insane.

Also David Allen Grier, a black comedian, was also known as D.A.G.

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