gTsang smyon Heruka (1452–1507) is one of Tibet’s most famous mad yogins. The mad yogins represent a relatively unknown aspect of Tibetan Buddhism that flourished in the 15th and 16th centuries. The mad yogins (and their disciples) claimed that they were following in the footsteps of the Indian Buddhist siddhas, and carrying out advanced Buddhist tantric practices by acting in unconventional and transgressive ways. Like some of the Indian siddhas, gTsang smyon started his religious career as a monk. When he was about twenty years old, inspired by a vision of his meditation deity, he suddenly started to act in a seemingly crazy manner. He left his monastery and spent the rest of his life wandering around as a homeless vagabond, practising a form of radical asceticism called “disciplined conduct”. Soon after he left his monastery, his antinomian and mad behavior led people to begin to call him gTsang smyon – “The Madman of gTsang”. Paradoxically, gTsang smyon’s crazy way of acting and dressing seems to have contributed to making him popular and successful. According to his hagiographies, gTsang smyon was supported by several powerful political leaders. This made it possible for him to accomplish the deeds for which he later became famous: compiling and printing the hagiography and song collection of the bKa’ brgyud master Milarepa (1052–1135); and also compiling an extensive collection of the Aural Transmissions of the bKa’ brgyud tradition. The most important aims of the present study are to describe how gTsang smyon was transformed into a mad yogin – a heruka – and to look at his subsequent activities as a mad yogin. The main sources on which the dissertation is based are three Tibetan hagiographies written by his disciples.