The legendary Genco, predecessor to Tom Hagen, and always the model of the perfect consigliere with unparallelled Sicilian
cunning, is only seen briefly in the films(I am not talking about the novel here). He is mentioned in GF I and appears in a deleted scene on his deathbed almost a supplicant, begging Vito to make some kind of deal with God to spare his life, and also in GFII as the son of the grocer who took young Vito in as long as he could. There was a brotherly relationship between young Vito and young Genco, but IMHO Genco comes off as kind of goofy. He's all infatuated with the girl who appears in the vaudeville show, and is otherwise clearly not Vito's equal intellectually or in the criminal world. He's a grocer's son and not much more. Vito's initial criminal dealings are with Clemenza and Tessio (and Roth in deleted scenes).

I can see Vito bringing Genco into the organization out of loyalty and so forth, but along the way Genco got really smart. What's the backstory there? How did he get from grocer's son, and brother figure to Vito, all the way to the greatest consigliere who ever lived?