The Riddler is probably the most annoying character in the history of comic books, he always speaks in a really high voice and giggles a lot. He doesn't even seem scary, just really annoying. He likes to tell riddles, jokes, parables, and play Words with Friends. If there was ever a criminal as annoying as this guy he would be punched in the face with regularity, and never really gain the opportunity to commit crimes. Batman also had a back-up villain used when the Riddler was out of material, called Cluemaster. He was just like the Riddler but lamer - he left notes at his crime scenes, but his notes weren't riddles, just typical crime scene drivel.
The Zodiac Killer is widely thought to have ripped off The Riddler, often taunting law enforcement with barely decipherable notes and cryptograms (much harder to understand and solve than the Riddler's riddles). Unlike the Riddler, the Zodiac killer was actually scary, capturing the nation's attention in the early seventies.Another killer, George Metesky, resembled the Riddler a lot, as he hid bombs all over New York City in the 40's and 50's, injuring fifteen people. He delighted in writing some really lame letters to local newspapers, which featured bad punctuation. see more on Riddler
Poison Ivy is a sexy eco-terrorist who uses plant toxins, and mind controlling pheromones to combat her opponents. She is immune to all plant poisons, which makes her a particularly deadly foe if you choose to do battle in campgrounds. Her character is said to be strongly aligned with the feminism movement, which makes sense, because she's very disgruntled. My theory is that she was developed as a character because Cat Woman was just really sexy and not threatening at all.
The first century Roman serial killer Locusta bore some resemblance to Poison Ivy. Locusta (whose name sounds extremely cool and scary) attempted to poison the Emperor of Rome at the time, Claudius, by serving him a dish of poison mushrooms. She no doubt was wearing something very suggestive at the time. She got a bit cocky after this, and colluded to poison some other fellows, before she was caught, and, according to legend, raped to death by a specially trained giraffe. People were so dramatic back then.Anna Marie Hahn was born in 1906 in Germany and immigrated to America shortly thereafter. A compulsive gambler, she began shacking up with older men, poisoning their food with arsenic, and either inheriting or stealing their assets thereafter. As if eating German food wasn't enough of a challenge already, imagine it with a dash of arsenic. see more on Poison Ivy
Few can forget Mr. Freeze's character. Wait, actually you can. He's kind of one dimensional, he only freezes things. Mr. Freeze apparently worked at a cryogenics lab before going crazy, although he wasn't a Dr. Freeze, so I guess he must have been a lab technician or something. Marvel Comics also have a character named Iceman, who is similar to Mr. Freeze except not as domesticated.Edwin Rowlette is a sort of real life Mr. Freeze. Much like Freeze, Rowlette was attempting to save his wife by using coldness. The real Mr. Freeze's wife was terminally ill, and, as he was working on her, he suffered an industrial accident and then apparently bought a big gun. Rowlette's wife, who had a history of health problems, was found in his Phoenix home lined with insulation and dry ice, along with several dead cats. Rowlette claimed that he was using the corpses for research, but it is assumed that most of his research involved drinking beer and watching The People's Court. I can kind of understand where he's coming from, however, because if I lived in Phoenix my dying wishes might very well be to be covered in ice the rest of my life as well, just to finally cool off. see more on Mr. Freeze