In 2269, he attempted to contact the USS Enterprise as it passed near Terra 10 to inform them that their planet was dying. However, with their great antennae buried, he was left with no choice but to use the colony's invasion defense to shrink the crew down to the size of 1/16 of an inch.
Once the crew of the Enterprise had shrunk down to the size of the Terratins, the Mendant ordered the bridge crew beamed to the Terratin city. When James T. Kirk later threated to destroy their city, the Mendant begged Kirk to save his people in exchange for all the dilithium the Enterprise needed to leave orbit.
After Kirk agreed and the Terratins, as well as their city, were saved, the Mendant and his people named the crew of the Enterprise "honorary Terratins, now and for all time to come." (TAS: "The Terratin Incident")