The Tolun are mentioned in Bolo Rising as follows:
"The Tolun were nonhumans, members of a very old species that maintained a trading and mercantile empire across much of this region of space."
“Two enormous golden eyes with jet-black, hourglass pupils blinked once, then twice again. The Tolun reminded Jaime , in a distant and somewhat warty-skinned way, of holographs he’d seen of an extinct Terran amphibian called a toad. Sshejevaalgh had the same rounded snout, the same bulging eyes rising above the same flat-skulled, golden-brown head. No toad had ever sported those writhing sensory tendrils sprouting from the side of the head, like golden angleworm-sideburns, though, and when he opened his mouth, the factor displayed a most untoadlike triple array of slicing teeth and stranger, less comprehensible mouth parts.”
“He - at least Jaime assumed it was a he, though he knew very little about Tolun biology - wore an ornately patterned robe or cloak, a jarring mix of reds, pinks, and aqua colors that, no doubt, was pleasing to Tolun visual senses but for humans was downright painful.”
The Tolun are sharp traders and always desire to learn new technologies even though their own is estimated to be considerably more advanced than present human technologies.