Aniello (Mr. Neil) Dellacroce was THE Underboss (there is only one). Big Paul Castellano was a capo whose juice derived mainly from being cousin and brother-in-law to Don Carlo Gambino. Carlo named Paul as his successor on his deathbed, passing over Dellacroce. Although Mr. Neil was such a traditionalist that he accepted the Don's decision, it created a resentment which caused a rift in the family, and led ultimately to Paul's assassination. Dellacroce remained Paul's Underboss until he predeceased Paul. Castellano's failure to show up at Neil's wake hastened his demise, a short time later.