Emilio (Season 1, Episode 1: "Pilot")
You never forget your first. Walter White's first step down a long, bloody road came under kill-or-be-killed circumstances. Forced during his first drug deal to reveal how he makes his superior product to Emilio and Krazy-8, two associates of his partner, Jesse, who have every intention of killing him once they find out the secret, Walt mixes up a lethal chemical cocktail in the back of his RV and seals them inside. This leads to both the frantic, gas-mask-and-tighty-whities high-speed flight down a desert highway that kicks off the series, and to his more gut-wrenching killing of a captive Krazy-8 later on (after he realized the poison didn't do the trick). Emilio, however, was the first person to die for the misfortune of meeting Walter White – and far from the last.