An insurance salesman with the mind of a detective, Walter Neff kicks off the top half of our list. Penned by Billy Wilder and noir mastermind Raymond Chandler, Neff is the perfect embodiment of early noir and the first on our list to fall tragically in love with a true femme fatale. He's also the sleaziest, most self-serving of any character to have made the list. Played wonderfully against type by rom-com favorite Fred MacMurray, Walter Neff is an insurance salesman with the intelligence and acumen of a detective. His co-worker, Barton Keyes (who is also played brilliantly against type by Edward G. Robinson, most famous for playing gangsters), recognizes his wasted potential and urges him to put his problem solving to use as a claims adjuster. Neff refuses, letting his desires set him down a slippery slope of criminal behavior. What's so much fun about Walter Neff, and Double Indemnity as a film, is that it defies you to root for the main character. Like any great noir protagonist, he knows the angles and knows what he's doing is wrong. Usually, a P.I. will find himself in the middle of murder and corruption accidentally, but Neff is the driving force of his own demise.