Dr. Death is Batmans earliest recurring foe, having debuted all the way back in 1939. He is also regarded as Batmans first proper super villain and was created by Gardner Fox and Bob Kane. An expert in all things poisonous, Karl Hellfern is your classic Mad Scientist archetype, although he has been presented in many different ways over the years. After his initial appearances (one of which had him as little more than a charred skeleton), Dr. Death disappeared from comics for about forty years. In an underrated 1982 story scripted by Jerry Conway and pencilled by Gene Colan, Hellfern reappears. This story re-tooled him as an entirely new character and presented the good doctor as a paraplegic who was terrorizing the city with various poisons. Eventually, following another long absence, the character was revamped yet again in the 2000s. This time around he was a terrorist (or at least a man who was happy to work for terrorists) and was depicted as wearing a trench coat and gas mask combination that, whilst somewhat generic, seems to really work for him. In recent years, Hellfern was brilliantly utilized by Paul Dini and Dustin Nguyen in their House of Hush story arc. His longevity was nodded to a number of times, especially as his schemes brought him into conflict with the parents of both Bruce Wayne and Tommy Elliot (now the villain known as Hush). Hellfern would also appear in both Tony Daniels Batman run and Grant Morrisons Batman R.I.P. Contrary to most of the characters on this list, Dr. Death has actually been quite in-demand over the last decade or so, so it is highly likely that well see him again relatively soon.