A good friend. In paticular a good left-wing friend. Taken from the slang term "Broseph", for brother, or close associate. This is combined with Stalin, in reference to Joseph Stalin, the former leader of the USSR(Soviet Russia).
Guy 1: "Hey there man, what's up?"
Guy 2: "Not much, how about yerself there, Broseph Stalin?"
Guy 1: "Not much dog, not much"
1. Many people know Joseph Stalin as a harsh and cruel dictator, but his closest friends (Bros) knew him differently. Recent photographs show Joseph Stalin sporting a bright red polo (a novelty at the time) double fisting 2 nattys watching two of his primo bitches wrestle for his attention. A voice recording shows Stalin calling the cold war "chill as fuck" and and even going as far as stating "shit I would lax if it wasn't so damn cold outside"
2. Someone who appears completely unchill and unbro, but takes on the full bro persona in the presence of other bros.
Man Sully's a real Broseph Stalin at work, but when the bros come over, the fists start pumping.