The son of an Anglican pastor, Carlisle was raised during a time of religious persecution. His father led hunts for witches, werewolves, and vampires all in the name of ridding the world of evil. As his father grew older, Carlisle was placed in charge of the raids. Carlisle wasn’t as enthusiastic about killing as his father was, but he was clever enough to discover a coven of true vampires living in the sewers of the city. He set a trap for the vampires and chased one down. Carlisle believes that the vampire was actually too hungry to run and consciously decided to attack. The vampire fell on Carlisle and left him bleeding in the streets after killing two other men and taking off with a third. (TW15)
Knowing how his father would react, Carlisle crawled into a cellar and buried himself in rotting potatoes for the three days of the change. When he emerged, he was a vampire. (TW15) At first he tried to destroy himself by jumping from great heights or drowning in the ocean. Somehow, he was so repelled by what he was that he resisted feeding off of humans. He even tried to kill himself with starvation. (TW16)
Eventually the thirst was too powerful and he attacked a herd of passing deer. He found that living off of the blood of animals could sustain his life and was infinitely more humane than taking the life of a human. Over the course of two centuries, he developed a sort of immunity to the scent of human blood and was able to become a medical doctor.
Carlisle's dad was one of those people who hunted supernatural creatures but Carlisle found a REAL clan thing of vampires and one surfaced and smelled the crowd but they thought that the vampire was so hungry that he just attacked and he bit Carlisle and Carlisle crawled away and turned into a vampire.
The Vampire who Changed Carlisle was never known (name, I mean).