Thor-Agena was a series of orbital launch vehicles. The rockets used the Douglas-built Thor first stage and the Lockheed-built Agena second stages. They are thus cousins of the more-famous Thor-Deltas, which founded the Delta rocket family. The first attempted launch of a Thor-Agena was in January 1959. The first successful launch was on 28 February 1959, launching Discoverer 1. It was the first two-stage rocket to place a satellite into orbit.
Among other uses, the clandestine CORONA program used Thor-Agenas from June 1959 until January 1968 to launch United States military reconnaissance satellites operated by the CIA. During this program, Thor-Agena launch vehicles were used in 145 launch attempts  now known to have been part of satellite surveillance programs.
Also, Alouette 1, Canada's first satellite, was launched on a Thor-Agena-B.