I had planned a post on this topic today, and by coincidence I find that FelixLeiter.com has posted a screenshot and some speculation about Felix Leiter in Quantum of Solace.
Who is Felix Leiter? In the novels, he serves some very useful literary purposes. He is Bond’s representative of America; introducing American lingo and culture to an unfamiliar audience (England and the U.S. being much more distant from each other in the 1950s than today). As a cheerful, sarcastic Texan, he epitomized America for Fleming; the opposite of the taciturn and typically British Bond. Giving Bond a companion also allowed Bond to explain things in dialogue to the audience, such as the rules of baccarat in the novel Casino Royale.
In the movies, Leiter has been less-defined. He is a chameleon, sometimes proper and stiff (TB, DAF), sometimes warm and companionable (NSNA, LTK), sometimes competent (TLD), sometimes a buffoon (GF). But what he has never really been in the films is a character.
With the return of Jeffrey Wright for a second film, it seems that Eon is finally interested in correcting that. Hiring a renowned character actor indicates Eon’s apparent intention to have some real personality for Felix (although it wasn’t evident in CR).
Who could Felix be in the films? A friend, surely, and also a counterpoint to some of Bond’s less worthy instincts. Of course, he also represents the resources and personality of the U.S., just as Bond represents the U.K., but if he isn’t a person, it’s just not as much fun.