Discoverer II successfully reached orbit and took photos of Earth. However, when the capsule with the data was ejected in order to re-enter the atmosphere there was a timer malfunction meaning it seperated too early and landed over the North Pole rather than the intended target of Hawaii. The capsule was never recovered.
Thor-Agena was a series of orbital launch vehicles. The rockets used Thor first stages and Agena second stages. They are thus cousins of the more-famous Thor-Deltas, which founded the Delta rocket family.