Greasy crooner and mob boss Don Corleone's (Marlon Brando) godson in the immortal 1972 film (and 1969 novel) The Godfather. Cause of him we have the infamous horse head in the bed scene and the "an offer he can't refuse" line.
Johnny (real crooner Al Martino) goes whining to the Don (Marlon Brando) to get him a part in a film that will save his career. The Don dispatches Tom Hagen (Robert Duvall) to persuade film producer Jack Woltz (John Marley) to see reason, by popping the severed head of Woltz's racehorse into his bed.
But the Don and Johnny go way back; years ago, the Don and right-hand henchman Luca Brasi (Lenny Montana) held a gun to a bandleader's head to help Johnny get out of his contract. Later in the movie, after the Corleone family muscles their way into a Vegas casino, they ask Fontane to appear there 5 times a year and persuade his show-biz buddies to also appear. Fontane is happy to oblige. The character and events are allegedly based on Frank Sinatra and his, again allegedly, receiving mob assistance in landing his role in From Here to Eternity.