In The Godfather, Tommasino is shown to be a close and loyal friend of Vito.
He helps Vito achieving his vendetta against Don Ciccio, and literally takes a bullet for him.
He hides Michael in Sicily after Sollozo and McCluskey hit.
However, as he left Sicily as a young child and returns there for the first time as an adult to perform his vendetta, I wonder how did he built a strong and loyal relationship with Tommasino?
It's not stated explicitly in the movie and the novel merely refers to Vito performing a great service for Don Tommasino
Michael had been transported from the ship docked at Palermo to the interior of the Sicilian island, to the very heart of a province controlled by the Mafia, where the local capo-mafioso was greatly indebted to his father for some past service.
...
The capo-mafioso was a man in his late fifties named Don Tommasino
The Godfather - Mario Puzo
