If needing another hero, perhaps King Voccio. Julius Caesar mentions him in the first book of the Gallic Wars as a Roman ally, and king of Noricum. Noricum had supplied Rome with high quality steel since the time of the mid-republic and continued to do so after their eventual annexation in 16 BC. Voccio had become king no later than 60 BC, and how long he ruled isn't known, but Caesar's mention of the king of Noricum sending 300 cavalry auxiliaries in 49 BC may refer to Voccio (though the man mentioned here is just called the king of Noricum; no name is given, so it may have been a successor). Voccio allied himself to the Suebian leader Ariovistus through a political marriage (Voccio's sister married Ariovistus as a second wife) and the two combined their forces to fight back against a Boii incursion (as the eastern Boii were being pressured to their own east by expanding Dacians), repelling a siege of the capitol of Noricum, an oppidum called Noreia.
His bonuses would be fairly straightforward. Celts in general were pretty well known for their mining and metallurgical prowess, but Noricum was exceptionally famous for it. A tech buff to weapon and armor stats, increasing them more than other Celts could get would work, emphasizing their superior metalwork that made them such valuable allies (could maybe apply to allies somehow as well, but maybe not as strong? Again, emphasizing the reason to align oneself with them). Or, alternately, if that's too broad, just make their javelins much more powerful than regular Celtic javelins. They used soliferrum. An aura for faster mining maybe. They were extremely prolific merchants, so some manner of trade bonus would be logical. Aside from metalwork they traded perfumes and aromatic herbs, alcohol, and woodwork, and their extensive trade networks into the north, through the Alps, kind of made them a centralized trade hub among Celts, so Voccio benefiting from exceptional trade makes sense.
Interesting aside about Voccio; despite Rome's eventual fighting with Ariovistus (in which the aforementioned sister of Voccio, Ariovistus's wife, was killed), it doesn't seem to have ever had a serious effect on Noricum and Rome's relations. Perhaps Rome viewed Noricum as simply too valuable, or viewed their alliance as a totally seperate matter. It was, afterall, in response to pressure from the Boii and the Norican kingdom needed assistance.
