Contagion/Legacy 

Someone should mention the "Contagion" and "Legacy" arcs in the article, as they're the storylines where Ra's al Ghul really ascends to supervillain status. They happened around 1996-1998. Ra's released a virus that wiped out about three quarters of the world's population. Batman would proceed to protect the cities that still contained humans (Gotham, Calcutta, Edinburgh, etc) against Ra's further terrorist attacks. Azrael and the Cult of St. Dumas also play a large part in the beginning of the arc. -