I disagree about the part of Neri being "an evil snake in all three films." He was conniving and duplicitious in II, to be sure. But he a practically non-existent role in the original and a minimal role in III. He was a force, no question, especially in the deleted scene where he kicks Klingman out of the casino that the Corleone's want to take over. And he certainly advanced himself in Michael's eyes past Hagen & Rocco.