The First Successful Spacecraft Rendezvous Was Between?
A space rendezvous is a specific orbital maneuver wherein two spacecraft (be they capsules, shuttles, space stations, or any combination there of) enter into the same orbit, approach each other at a very close distance, and maintain orbital velocity for a period of time. Docking or berthing of two crafts together is not required to qualify for a successful rendezvous.
Working within those parameters, the first successful space rendezvous was between the Gemini 7 and Gemini 6 space capsules on 15 December 1965. The pilot of Gemini 6, US Astronaut Wally Schirra, artfully maneuvered the capsule to within one foot of Gemini 7 and maintained the same orbit and velocity for over 20 minutes.
The next notable space rendezvous after the Gemini pairing came in 1966 when Neil Armstrong performed the first space docking when he docked Gemini 8 to an unmanned Agena Target Vehicle. The Agena, as its name implies, was a spacecraft designed expressly to help the Gemini Astronauts practice orbital docking maneuvers in preparation for the Apollo moon missions.
Gemini 7 seen from Gemini 6; photo courtesy of NASA.