Crowley used to be a crusader in the 13th century and was considered a hero. He believes in God until the reality of war and unanswered prayers changes him. When his commander dies, he stops praying to God. Even then, he still hopes for God to do something and even touches his commander's rosary until becoming a vampire.
Crowley first encounters a tan dark-haired vampire during the Crusades. Although Ferid is also there, Ferid does not talk to Crowley until years later. Ferid began watching for Crowley approximately 150 years before he turned Crowley because he was waiting for someone with the Michaela trait.
Ferid drives Crowley to hate him and thus remember his face before using Saito's blood to turn Crowley into a vampire. When Crowley finally hunts Ferid down decades later, Crowley's human feelings have waned to the point where he does not recall why he wanted revenge on Ferid, and he becomes Ferid's comrade. Crowley later says he joined Ferid Bathory's faction because Ferid always makes things interesting.