A very tall humanoid species with large, double-domed bald heads, devoted to pure research, who sent the negotiator Leyor to bid for the Barzan wormhole before withdrawing from the talks.
The Caldonians are introduced in the Next Generation episode The Price. They stand well above human height, with a hairless skull divided into two prominent lobes and hands with fewer, thicker fingers than a human's. Their culture prizes scientific research above commerce.
In 2366 their representative, Leyor, comes aboard the Enterprise-D to compete with the Federation, the Chrysalians and the Ferengi for the rights to the Barzan wormhole. The rival negotiator Devinoni Ral persuades him that administering a wormhole would only distract his people from their studies, and Leyor pulls out, throwing Caldonian support behind Ral's clients.
The wormhole then turns out to be unstable, so the withdrawal costs them nothing.