やる

[Vagrere]

I was wondering if somebody could explain to me what role, precisely, やる fills as a suffix verb. My dictionaries haven't offered a particularly convincing explanation, but one definition in particular, as well as the context I see it used in, suggests to me, at least, that it's a less polite way of saying あげる. No idea how accurate that supposition is, though. Thanks in advance, etc.

[Akihiko Yamamoto Hozagaki]

Finally! A question I can answer!

やる is used when the receiver of the action is of lower social status than the giver. Like, the giver's younger brother. I hope that helps you out!

Oh goodness I hope I'm not wrong O_o.

[Vagrere]

Well, yes, I kind of figured out that much from various definitions and context. I'm wondering what the precise meaning of the suffix is, though.

[Akihiko Yamamoto Hozagaki]

It has the same meaning as あげる, I believe. No difference otherwise.

[AzureDark]

Keep in mind that it's not interchangeable with -every- instance of 'ageru' though. This is only in the case of '-te ageru'. Another one that you can replace with it is 'ataeru', though it's rarely used.

'yaru' in itself is a generic 'do'. You might find out that 殺る is 'yaru', which is to "do" someone. Thus 殺ってやる and 殺してあげる means the same, if you take out politeness context.

[Datenshi]

Thus 殺ってやる and 殺してあげる means the same, if you take out politeness context.
You'd have to stretch your imagination a bit to think of a situation where politeness is called for when you're offering to kill someone, though XD

Your question has pretty much been answered above, but I'll add that やる as a suffix can in some cases be used to connote a positive attitude towards an action.

For example,
やってやる！　-> I'll (definitely) do it!
勝手やる！　-> I'm going to win (no matter what it takes)!
殺してやる！　-> I'm going to kill you (for sure)!

You'll simply have to rely on tone and context to distinguish this from the usage of やる AzureDark-sempai stated above.

So in a nutshell,
やる (as a verb) -> give, send for
～てやる (as a suffix) -> do ~ for someone
～てやる　(as a suffix) -> attatches a positive attitude towards an action