MULDER Meaning of MULDER in English Mul ‧ der, Fox /ˈmʌldəʳ/ BrE AmE the main male character in the US television programme The X Files , who is an ↑ agent for the FBI, and who believes in ↑ alien s Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012