He was born in the same neighborhood as Pete Clemenza, whom he always admired, and who eventually became his mentor in the family.
In 1955, he becomes a made man and enters Clemenza's regime. After Clemenza's death in 1958, he joins Frank Pentangeli's regime. After Pentangeli commits suicide in 1959, Nobilio becomes the new caporegime. From then on, he is Michael Corleone's top earner and one of his most trusted men on the streets.