Mulder was born on October 13, 1961 in Martha's Vineyard, Massachusetts. The mysterious disappearance of Mulder's sister and his ensuing search for her became the consuming drive of his life. In 1983, Mulder graduated with first class honours from University of Oxford with a Bachelor of Arts degree in psychology. He then graduated with honors from the Quantico FBI Training Academy in 1986. Mulder joined the FBI on October 24, 1984. On graduating from the Academy, Mulder began his work in the Behavioral Science Unit (psychological profiling) under Agent Bill Patterson, with whom he had a testy relationship.