Good-boy-gone-kind-of-bad, Linmar Ponyets is a trader with the Foundation. He once was a member of the seminary, training to become a priest, but the Fathers couldn't deal with him (so he says), and they gave him the boot. Ponyets has all the major character traits of a Foundation protagonist—just a smaller story.
Anti-Tradition + Innovation (Check)
Like Hardin, Ponyets isn't limited by custom and tradition. When trading with the Grand Master and then Pherl, he's supposed to be trading technology to help the Foundation access Askone society through religion.
But the religion on Askone deems trade in technology as sacrilege, and, well, that's a conflict. So, Ponyets adapts. He doesn't trade in religion or technology (at first)—he trades in gold. As he mentions when presenting the gold to the Grand Master: "Come, I don't offer the machine. I offer the gold" (IV.4.29).
Ponyets gets that custom and tradition won't work on Askone, so he invents a wholly new method of dealing with the solution—just like a true protagonist.
Rational Decisions + Technology For the Win (Check, check)
With innovation comes rational thinking and decision-making. Like Hardin before him, Ponyets is quiet but deadly. He uses rational thinking to outmaneuver everyone else in the story, deducing that the Grand Master wants gold and isn't going to ask too many questions about where it comes from. Then, he traps Pherl by understanding Pherl's needs and knowing that the transmuting device will be perfect bait.
He also out-thinks Gorov, his fellow Foundation man. Ponyets recognizes that Gorov will "come back and try again" to sell technology laced with spiritual connections (IV.3.16). He'll use the same strategy over and over again until it either succeeds or he dies. Not fond of taking the death route himself, Ponyets rationally decides that a new method of attack is required, forcing him to innovate (see how the two are so tightly connected in the novel?).
Finally, Ponyets uses his knowledge of technology to get ahead. Using technology, he whips up a gold transmuting machine and implants it with a video recording device. He clearly has the technological upper-hand in every situation he encounters—which means that he also has the upper-hand in all of his political and social negotiations as well.
Okay, we're not really sure about this one. Ponyets isn't a leader of the Foundation like Hardin and Mallow, so he doesn't have to make a decision about whether or not to go to war. In fact, he's never presented with a challenge where violence is really a possible solution, and no one pressures him from the sidelines to pursue violent means like a Sermak-type character.
But he is against the idea of Gorov being executed, and we have to figure that, if he could whip up a gold transmuting machine out of spare parts, he probably could have managed to create a pretty devastating weapon. But he didn't. Sure, it's a bit speculative, but we'll count it: Ponyets is another nonviolent protagonist.