He wrote under many different pen names, including Capitain Ramon Diaz de la Escosura, M. Gisela, Hobble-Frank, Karl Hohenthal, D. Jam, Prinz Muhamel Lautréamont, Ernst von Linden, P. van der Löwen, Emma Pollmer, Richard Plöhn, and Oberlehrer Franz Langer.
May invented the characters of Winnetou, the wise Indian, and Old Shatterhand, Winnetou's white partner.
His works were immensely successful in Europe, translated into 33 different languages and selling over 200 million copies, yet he is virtually unknown in the English-speaking world - though this is slowly beginning to change. Several of his novels were subsequently made into films.
Even long after his death May is blamed for Hitler praising his works (but Albert Einstein, Hermann Hesse and Bertha von Suttner praised May also).
May also dabbled as a musical composer, writing two very famous romantic German songs, "Forget Me Not" and a version of "Ave Maria."