Just my rambly thoughts about Clint, mostly in relation to the fic universe I'm working on and the headcanon I've built up.
ETA: This is a mash-up of the last three months of fic, discussions, and general feels as well as some stuff cherry-picked from comics canon and observations from the movie(s). I make no claims to the originality of any particular point, and have been main-lining fanworks since I hit this 'ship so I've read so much I couldn't begin to list where ideas might have originated from. But I <3 every single person who's stuff I've run across and the AMAZING fanon/'ship we're kind of collaboratively building here. This is the BEST 'SHIP!
Clint:
I accept the basics of the comic-verse backstory (up to a point) - yes, he had an older brother, their father was a raging abusive alcoholic, and their parents died through tragic circumstances (that his father was probably directly or indirectly responsible for). They go through foster care and run away to the circus, which is also a pretty abusive environment (but worse for Barney than Clint, actually, because Clint's accuracy has always been very good and they kept the two of them on because of it. Barney was more expendable or somesuch, plus I think he deliberately deflected some stuff away from Clint to help protect him.)
The circus they ended up at (my headcanon, here) is an aging, threadbare kind of place, and many of the denizens are older and came over to the US from post-WWII Europe. So Clint learns several languages as a kid (like German and Russian and Romany) as well as acrobatics, climbing, knives and the bow and arrow (and being able to read and con people.)
He has no problem with killing people who he decides need to be killed. Those literally don't bother him. He's got a real issue about innocent collateral damage, though. Something happened in his past (probably while he was with the military) that had a high civillian body count that he got busted for - and was something that he was responsible for, but it was because he went with someone else's lead or orders. Part of his agreement with Coulson when he's brought into SHIELD is that he makes the final call about taking a shot or not. (This is reflected both in what Natasha tells Loki and his conversation in Thor with Coulson.)
I get the impression that Fury thinks (now) that he's a valuable asset but doesn't like his approach or methods very much. He thinks Clint is too much of a wildcard and I think he suspects if not outright knows that SHIELD isn't Clint's first loyalty. (That would, of course, be Tasha.) He's not thrilled by Clint's approach to keeping an eye on the cube, and Natasha seems much more focused on the "getting Clint back" part of the whole equation than Fury does. (Which makes perfect sense, mind you.) That same scene in the cube room also shows us that Clint's extremely intelligent and a bit of a lateral thinker - it doesn't occur to Fury or even Selvig that something on the other side of the cube might be triggering it, Clint's the one that brings it up. My headcanon has Fury really questioning Coulson's decision to recruit Clint in the first place and then again Clint's decision (which Coulson backs up) to bring in Natasha.
Clint's *extremely* dangerous. He can hold his own in hand-to-hand or knife combat with Natasha (though she's still slightly better). VERY VERY few people can do that. He's had Special Forces training along with Sniper training along with the training from his childhood that he's kept up. In particular, I think it's the acrobatics training that helps him keep up with her so well, I think that lets him think in more three dimensional space during a fight than other styles/skills might by themselves. He's just as good and accurate with thrown objects and firearms as he is with the bow.
He prefers being the eyes on the scene and to "direct" traffic than be in the middle of the chaos - it's that trying to minimize innocent deaths thing again - this is also echoed a bit in him trying to get the kids out of the bus in the Battle of Manhattan. He's got a thing about kids, in particular and protecting them. Natasha thinks it's going to get him killed one day, and probably her, too. Deep down, it freaks him out just a little (or did at first) when it looked like she was being "reckless" during a fight/mission (things like jumping onto the Chitauri ship, etc) but he has that streak himself (hello, jumping off a building) so he kind of has to accept that and try not to worry about it too much. Plus, the longer they're partners, the more confident he is that she'll make it out of whatever seemingly unlikely situation she's gotten herself into.
He's vaguely agnostic if he's anything. He accepts the possibility there might be something more out there but doesn't spend much if any of his time thinking about it. I think he was probably surrounded by some level of old European Catholicism growing up with a heaping dose of some superstition mixed it. Most of it rolled off of him, but there's a tiny bit of nostalgia there. He likes western European style cathedrals - the scope and architecture of them, and the atmosphere.
When it comes to undercover work, it's not his first choice (though occasionally depending on the cover it can be fun) but he's really damn good at it, regardless. He hadn't really done any kind of deep cover "spy" kind of work before Natasha, but she kind of takes him in hand and teaches him how and he's a quick learner. It helps that he's really good with languages. His off duty clothing preference tends to casual clothes (t-shirts, jeans, jackets, boots) but he's equally at home and comfortable in BDUs or in a hand-tailored Armani suit when he needs to be. All this comes again, from my idea that he's Natasha's perfect foil - and to be that he *has* to be adaptable.
When he's just himself, I fall into the Classic Rock/beer take on him - casual Americana of someone who grew up in the 70s/80s in the American South and Midwest. I get that he loves fast cars and flirting as a casual endeavour when it's not going to cause problems, and likes a good bar fight on occasion, just because. He can cook, but relatively simple stuff because that's what he likes so that's what he learned. He's the better driver of the two of them, but not by much.
He likes using a bow not just because it's familiar and inherently his favorite (though it is) but also because he likes that it causes people to underestimate him a lot of the time. It looks "quaint". The weapon itself is underestimated, and because he chooses to use it, people are more likely to think he lacks a high level of skill with a firearm or that he's as serious an agent or fighter.
I lean more towards silent, occasionally snarky, always smooth Clint as opposed to goofy class clown Clint. Oh, he'll play pranks, but good luck ever proving it. ;)
He's been with women before, but if any of them were relationships rather than one or two night things, they didn't last very long - mostly because of the type of work he's always done. There was probably a girl in high school he had an unrequited crush on, or maybe some kind of summer thing in a town the circus was passing through, but nothing that was long term or serious. He loves and respects women, enjoys being with them, he just hasn't ever had the combination of the right person and the right time to be really serious about one before. (Until Tasha of course.) He doesn't *need* to be with a woman, per se, but has always found it enjoyable in the past if the opportunity for some fun presented itself. (Again, until Tasha.) In the past he was circumspect enough about his activities that his fellow soldiers or SHIELD agents just assumed he wasn't getting any and would occasionally rag on him about it. He tends to ignore that kind of thing with either a grin or an arched eyebrow depending on if the person is a friend or trying to be mean about it.