Spock One was a holographic recreation of Ambassador Spock created by the Romulan Sela in 2368. She obtained his image for use in the program during meetings between the real Spock and Proconsul Neral. The program was not interactive and was unable to respond to questions.
Sela created it to be used in the event of Spock refusing to read a statement encouraging the Vulcans to welcome a peace envoy from Romulus. The peace envoy was a plot to send the Vulcan ships, full of Romulan troops, to conquer Vulcan. It was not used, however, due to the intervention of Spock, Data, and Captain Jean-Luc Picard. (TNG: "Unification II")