The Unearthed Arcana barbarian was famously over-powered and over-described. I'd rather have something much simpler, especially for OD&D. What's the minimum amount of mechanics that could give a standard fighter the feel of a barbarian?
I'm thinking that the berserker in the Monsters & Treasure book is a good place to start. The LBB berserker is much simpler than some later versions: they don't roll for morale and they get a +2 on attacks versus normal men. No real "rage" mechanic, just acknowledgment of their ferocity versus civilized troops. In fact, I interpret "normal men" here as excluding 1st level characters.
For a slightly more "ferocious, uncivilized, magic-fearing" barbarian, I think I'd go with:
- no morale rolls except against magic;
- +2 on attacks vs. normal men or spell-casters;
- -1 reaction from civilized people;
- can't start with literacy, must learn it (counts as a language.)