I'm in a pinch in which the thesis of my essay requires an old, OLD Hercules story to back it up. It's too late to scrap everything I've already written so I'm wondering what the oldest, full story of Hercules is and where I can find it. All help is appreciated! Even if it's not the oldest, I'd still love to know the oldest one you know of personally, I am really just trying to get a story as old as possible, but any full stories are extremely appreciated!
Mentions of what we know as the labours of Herakles appear as early as Hesiod's Theogony (8th c. BC, slaying the Nemean lion, specifically), but only in brevity. Other old mentions include Euripides' play Herakles (5th c. BC). As far as I know, the oldest full story of the twelve labours is the Bibliotheka of psedou-Apollodorius which is comparably late, its compilation dating to the 1st or 2nd century AD.
You might also want to look at other Indo-European deities with similar characteristics, in particular, the vedic deity Indra, who is treated extensively in the Rgveda, which dates to the mid-2nd milennium BC.