James Bond was an alcoholic, with good reason. He didn’t drink vodka martinis for the taste, he drank them to dull the pain and horrors of his job. As much as he drank, he probably didn’t really taste the booze anymore.
The original James Bond from the novels was a dark and brooding high-functioning alcoholic, who operated at his best with a drink or two in him at all times. He was pretty useless without the drink. A vodka martini would quickly get him in the right headspace to accomplish his latest mission.
The movie Bond was reinvented to be this dashing, handsome womanizer who drank and smoked socially and was charming as hell. Basically, a 1950s ideal male fantasy. This Bond probably could’ve used a classier drink than straight vodka, but that’s one aspect of the books they kept pretty loyal.
The Vesper is James Bond’s personal invention, from the very first novel, Casino Royale. It’s basically his own custom twist on the vodka martini.
He explains he only has one drink before dinner, but he prefers it’s a large one, ice cold, and made very well. He drinks plenty of other types of alcohol throughout the books, but he’s pretty particular about this one evening aperitif.
The movies kind of latched onto it and just made him drink vodka martinis in general. Although the 2006 film Casino Royale had him order his custom invention from a bar, almost word-for-word from the original novel. It’s named after Vesper Lynd, the first girl Bond truly fell for in the novels.