Frankie Toscani was an active member of the Toscani crime family in New York City. He was involved in a feud with some Russian mobsters working out of Coney Island, and hit them pretty hard. So the Russians decided to hit back.
They seduced Frankie with a beautiful woman, and knocked him unconscious. When he awoke, he was tied to a chair and naked. A large Russian man was holding garden shears and a big smile, and told him they were sending a message to the Toscani family. Then he cut off Frankie's penis.
When he got out of the hospital, Frankie implored his father to avenge his mutilation, but the elder Toscani wouldn't have it. He made some excuses about how the Russians were too strong, or it wasn't the right time, but the truth was that his son had been unmanned. And a disgrace to the Toscani family.
After that, Frankie was an outcast. The only person who talked to him was his sister, who taunted him by calling him names such as "Eunochio." So Frankie shot her husband, which caused even more bad blood. Eventually, he left the country and started doing freelance jobs.
That's how he ended up at Masada, the headquarters of The Grail. He was contacted by Starr, the Grail's Sacred Executioner, who had a special project for Frankie. Starr had captured a vampire named Cassidy, who was exceedingly difficult to kill. He wanted Frankie to go into the holding area with his gun, and see just how much punishment the vampire could take.
Frankie reveled in the job. He brought an authentic Lee-Enfield bolt action rifle, the treasure of his collection, and took casual shots at Cassidy, blowing off bits and pieces at his leisure.
When Jesse Custer arrived to rescue his friend, Frankie was prepared. Starr had told him all about Custer's Voice of Command, and was ready to shoot as soon as Jesse said a single word. Unfortunately, the word Jesse used was, "Miss."
Frankie missed the shot, and Jesse knocked him down into the pit where he had been shooting Cassidy. His neck broke, all Toscani could do was lie there while Cassidy drank his blood to replenish his strength.