Everything about the Cullens began with Carlisle Cullen, born in 1640, London, England. He is also the leader of the Olympic coven. Carlisle was the son of an Anglican pastor who used to actively go on hunts for witches, werewolves, and vampires. After taking over his father's role, he was bitten in an attack, turning him into a vampire. He began studying at night and became a profound doctor. Carlisle practiced his profession in Columbus, 1911, where he treated a patient, Esme Anne Platt, a teenager who broke her leg falling out of a tree.
In 1918, he was directed to do all in his power to save a dying woman's son, Edward from the influenza. Thus the start of the Cullen family, they moved to Ashland Wisconsin. Here Carlisle re-met Esme after a failed suicide attempt, he turned her into a vampire to save her life. When she awoke they spoke of their encounter in the past and began to quickly fell in love.
Next to join the family was Rosalie, who was sexually and physically abused by her husband and his friends who left her on the street to die. Carlisle could only hope that her and Edward would become potential partners, but neither saw eachother as so, remaining adopted siblings.
When Rosalie was hunting, she came upon Emmett McCarty, he had been in a bear attack and likely wouldn't make it as human. She carried him for over 100 miles to her father to turn him.
Mary Alice Brandon and Jasper Whitlock united with the coven in 1950, which Alice forsaw with her visions abilities. In the Cullens, Jasper and Rosalie pose as twins using the surname "Hale".
Eventually the family moved to Forks, Washington where they established a treaty with the Quileute tribe to agree on either parties' peace if the Cullens did not bite humans(to kill or turn), or trespass their land.