The Agena test vehicle was an unmanned spacecraft that was in service to NASA in the mid-20th century. This vehicle was used for developing and practicing orbital rendezvous between spacecraft in the Gemini Program. This was an essential step in the preparation up to the Apollo program. The first successful docking of an Agenda test vehicle to a manned spacecraft occurred on March 16, 1966 during the Gemini VIII mission.
In 2267, there was a picture of this historic spacecraft in Commodore Stone's office on Starbase 11. It was located to the right of the transporter alcove. (TOS: "Court Martial")