Vincenzo Pentangeli was the elder brother of Frank Pentangeli.
Vincenzo was a native of Partinico, Sicily, and remained there when his brother went to America. He was believed to have been involved in the Sicilian Mafia. Frank urged his brother on several occasions to come to America, however, Vincenzo opted to stay in what Frank described as a "two-mule town".
In 1959, Michael Corleone got word that Frank was going to testify against Michael before the Senate. Michael briefly considered having Frank killed, but realized he was too heavily guarded for this to be a realistic option. Michael instead had Vincenzo flown in from Sicily. Vincenzo's presence at the hearing was to warn his brother against testifying and thus breaking the code of omertà. The two brothers exchanged a glance before the hearing was called to order. It was enough for Frank to get the message, and he recanted his testimony, blowing apart the government's case. Vincenzo was returned to Sicily soon afterward.
In the video game
In the video game, Vincenzo was intercepted by men loyal to Hyman Roth who planned to eliminate him and prevent Michael from gaining success in the hearings, but Dominic Corleone managed to interrogate one of the men as to where they were keeping Vincenzo. Dominic eventually hunted down and killed the men responsible and was able to return Vincenzo to safety.
Here he speaks English, whilst it was stated he could speak none in the movie, but this is not mentioned anywhere in the game; he could also have been only pretending to be unable to speak English in the trial.