Though a tyrant is a cruel dictator in modern language usage, the original meaning had no negative connotations. It simply meant that the ruler had obtained his position through his own strength and intelligence, not through inheritance.
Sophocles' famous play Oedipus Rex literally translates as "Oedipus the Tyrant," and is even occasionally titled Oedipus Turannos, because Oedipus gained kingship of Thebes after solving the Sphinx's riddle. The title, of course, is ironic, because Oedipus demonstrates his headstrong ignorance in spectacular manner.