Gerhard Hendrik Armauer Hansen ( July 29 , 1841 - February 12 , 1912 ) was a Norwegian doctor and scientist who was famous for discovering the bacteria that causes leprosy in 1873 . Gerhard Henrik Armauer Hansen ( 29 July 1841 â `` 12 February 1912 ) was a Norwegian physician , remembered for his identification of the bacterium Mycobacterium leprae in 1873 as the causative agent of leprosy .