WMG / Taxi Driver

Tom Neville from Revolution watched the film at one point.
In the episode "Clue", Tom compares John Sanborn to Travis Bickle of the film. Admittedly, it wasn't the best comparison. That's the downside of analogies...when you apply critical reasoning to an analogy, you can poke a lot of holes in it by pointing out the differences.

Travis' dad is George Bailey from It's a Wonderful Life.
This is a rare example of a Wild Mass Guess that somebody outside TV Tropes has thought of: the film critic David Thomson wrote a novel called Suspects which drew imaginary connections between movie characters, and one of them was that little Tommy Bailey, one of George's sons, grew up, joined the military, served in Vietnam, was wounded and returned home, and the experience changed him so much that he changed his name from Tommy Bailey to Travis Bickle. George is basically an idealist who wants to do the right thing by people, but the endless frustrations of his life drive him to despair and thoughts of suicide, and it's only when the people in his small town rally around him and show him how much he's loved that he recovers his good humour and appetite for life. Travis is also an idealist and there are strong hints that he's a Midwesterner like George, but he has no real friends and he doesn't belong to a community. His frustrations drive him over the edge: he projects his own alienation onto the (admittedly very alienating) city around him, and in the end he chooses the target of his violence purely for reasons of opportunism. He can't get close enough to Palatine to kill him, so he goes after Sport instead, who doesn't have Secret Service protection.

The passenger who tells Travis that he wants to kill his wife doesn't exist
This, like the above entry, has also been proposed elsewhere. It has been theorized that this character was imagined by Travis, and represents the deep recesses of his mind.

Travis is Holden Caulfield
This might be a stretch, given the conflict in timelines (Holden is already about 17 in Catcher In The Rye, which takes place in the late 40's to early 50's, and would be older than Travis if we assume the two works follow the same timeline). However, there are still enough similarities to argue this case. In Catcher, it is shown that Holden's relationship with his parents is strained, as he does not think to call them even while at his loneliest while alone in New York. Knowing this, it's possible that as Holden got older he grew more and more apart from his family to the point where he changed his name to Travis Bickle. Holden is a depressed, cynical, mentally unstable loner who feels disconnected from the world around him and scorns his surroundings as "phony." The same thing could be said about Travis, only on a much more severe level. As Holden has gotten older, he has become more unstable, and the objects of his scorn have moved from the "phonies" in his world to his obsession with vigilante justice and "cleaning up the human trash" in the city. Holden also has been shown to be unsuccessful with women in his personal life, a pattern mirrored by Travis, as he botches his second date with Betsy by taking her to a porno theater. This gaffe is considered less socially acceptable than any of Holden's gaffes, but it can be argued that as his mental instability increased, so did his feelings of isolation, and as a result, his social ineptitude. Travis's desire to protect Iris's innocence mirrors Holden's desire to protect the innocence of his younger sister Phoebe, and children in general. My theory is that the reason Travis is so drawn to Iris when she's really just a random prostitute who spent all of 10 seconds in his cab is because she reminds him of Phoebe. It could be that she looked like her, her voice, or even the way she carried herself. The fact of the matter is that she must have struck a chord with him on a personal level that wouldn't have been possible if she were just some random child hooker.

Going off the point above, Taxi Driver is actually a modern, R-rated version of Catcher In The Rye.
While there may not be enough evidence to argue that Travis is the same person as Holden, there is still enough evidence to argue that Scorsese may have been inspired by the book
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