It's unikely that people wake up one day and say "I think I'll become a manager of a band/singer/songwriter". Most successful managers have fallen into their jobs by being in the right place at the right time finding or being found by someone whose talent they believe in. They lose their own lives and their life becomes so entwined with their artist often to then be discarded once success has been established. Hear their stories - always interesting.
Possible speakers could be Tom Watkins who managed Pet Shop Boys and Bros; Nigel Martin-Smith original manager of Take That and Tony Smith, manager of Genesis.