It was discovered in 1952 after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to hemophilia.
A sample of his blood was sent to the Oxford Haemophilia Centre in Oxford, where Rosemary Biggs and R.G. McFarlane discovered that he was not deficient in Factor VIII, which is normally decreased in classic haemophilia, but a different protein, which received the name Christmas factor in his honour (and later Factor IX).
The O'Reilly Factor | The X Factor (UK) | Microphthalmia-associated transcription factor | The X Factor | Fear Factor | Max Factor | The X Factor (TV series) | B-cell activating factor | Epidermal growth factor receptor | Psi Factor: Chronicles of the Paranormal | Astro Boy: Omega Factor | twist transcription factor | The X Factor (U.S.) | The X Factor (UK TV series) | The X Factor (UK series 2) | The Omega Factor | The Butch Factor | The Adonis Factor | Sp1 transcription factor | Rheumatoid factor | PSI Factor | O'Reilly Factor | Insulin-like growth factor 1 | Factor Three | factor | ETX (form factor) | epidermal growth factor receptor | Britain's Got the Pop Factor... | Vascular endothelial growth factor A | The Vengeance Factor |