This is a mere speculation, but I have many reasons to state the following considerations. People is used to think that Archer and Shirou are completely original characters (or well this means that Archer not being an historical heroe or well known character who has a legend behind) isn't inspired by any other fictional or real person.
I don't really think so. I strongly believe Archer got some traits from one of the most famous archer ever, or well Richard/Dick Shelton, the protagonist of the well-known book by R.L.Stevenson The Black-Arrow. How so?
Well I suppose my opinion is completely subjective, since that book is one of my favourite ever (pluggage a part, I also have a domain with its name sake), but I find many elements in common between these characters, although the setting and the story are very different. Richard begins his adventure as Shirou does, he's naive and he trusts too much people till the extent he isn't able to understand that sir Daniel (the person who's looking after him, since his parents died) is just using him as his puppet (this doesn't happen with Kiritusgu, but just think that he's the person who involved Shirou in the war, through Avalon). Richard can't really understand the situation he's into and he can't even realize the thin difference between good and bad, and even him, we can't really say he's a completely positive figure too. Richard gets into troubles by meeting Joanna (as Shirou does as he meets Saber), who let him understand he's being betrayed by the person he trust the most. At that point Richard needs to make a choice (as Shirou at the beginning of the story) and he decides to stop the activities of those who're acting against his people and his nation (and Shirou decides to stop that cruel game called "Grail War") and joins the group of the Black Arrow, whose arrows are indeed black, to punish the evil ones (Shirou joins the war to stop it and Archer's clothes are black, since he's taking a sort of revenge). Richard isn't only an archer (although he's clearly a good one) but he's also a knight (and as you can notice Shirou and Archer are like him) and he's a very good fighter who shows his valour during the war of the Two Roses (the Grail War can be associated to it, under a certain point of view). He fights for people, but mainly for himself, to heal his honour, to take his personal avenge and most likely to save his true love from the one who betrayed him (as Shirou does with Sakura). Richard could be considered more similar to Shirou, but I think he's even more similar to Archer. Shirou couldn't bare the guilty feeling of doing something wrong against people, Richard does instead, and as Archer he can punish people without thinking twice about it.