The Vians were a technically advanced race that were first encountered in 2268 by Starfleet. They were encountered on the second planet in the Minaran system.
Two of them were encountered by members of the U.S.S. Enterprise crew on the planet. The members were captured by the Vians and experimented with.
The Vians wanted to test a female inhabitant from one of the planets in the Minaran system. They wanted to do this because the sun was about to go nova and and the Vians could only save one of the planets.
The wanted to test the female inhabitant the will to survive, love of life, thirst of knowledge, and to sacrifice her own life. These values were taught to her by torturing the three members of the Enterprise crew, Captain James T. Kirk, Commander Spock, and Doctor Leonard McCoy.
The Vians did not believe that her race was worthy of survival. This is why they tested her to see if her self-sacrifice could be stronger then her instinct for self-preservation. Captain Kirk persuaded the Vians that they had lost the capabilities to experience the the feelings they had been trying to feel. They agreed and took the telepath with them.