who is the most powerful mafia don in american history? is it lucky luciano, gambino....who? thanks for your help. also have any of you heard of a guy named vito casiefero?

It's hard to quantify "most powerful," since none of them ever filed a tax return or issued an annual report describing their work force, main businesses and assets.
Charlie Luciano would make the short list because he formed the Commission in 1931,and in effect, was its chairman. He was also the first "modern" Don (as opposed to a "moustache Pete"). Frank Costello probaby had more political power than any Don in history, and IMO was the model for Vito Corleone. Carlo Gambino's family was the most powerful in America, and took in more money than any other; Don Carlo never went to prison and died peacefully--two major marks of success.
Don Vito Cascio Ferro can be said to be the "Godfather" of the godfathers--he was a powerful Sicilian Don of the early 20th century who forged ties with American Mafia families and had great influence with some of them. But he was not a big power in America.

What do you mean by "Moustache Pete"?

Moustache Pete just generally refers to the old time bosses. Not keeping up with the times etc. Depending upon which generation of Mafia wiseguys your talking, I'm sure most will talk about their predecessors as Moustache Pete's, but generally the real Mustache Pete's were Joe the Boss Masserria and Sal Maranzano.

I would like to name the Don Pablo Escobar. The one who made billions of dollars from American coke heads, Pablo controlled 70% of all the world's cocaine supply at that time. He was serving prison in his own castle, guarded by his military army. With tremendous political power, he was even elected to a seat in the Colombian congress. By 1989, Forbes magazine listed him as the seventh richest man in the world.