The Centaur rocket is a high-energy upper stage designed for use on satellite launch vehicles, boosting the satellite into its final orbit or, in the case of interplanetary probes, to escape velocity.
Centaur was the brain child of Karel J. "Charlie" Bossart (the man behind the Atlas booster) and Dr. Krafft A. Ehriche, both Convair employees. Delopment started slowly in 1956. The first (unsuccessful) test flight was in May 1962. The first successful flight was some 3 years later.
Centaur uses an ingenious common double-bulkhead to separate the LOX and LH2 tanks. The two stainless steel skins are separated by a .25 inch layer of fiberglass. The extreme cold of the LH2 on one side creates a vacuum within the fiberglass layer, giving the bulkhead a low thermal conductivity, and thus preventing heat transfer from the reasonably warm LOX to the super cold LH2.
A version of the Centaur was developed for use with the Space Shuttle but was never used due to tougher safety rules imposed after the Challenger accident. This decision helped led the US Air Force to create the Titan IV, which uses the Centuar as its final stage, to launch payloads which had originally been designed for the Shuttle-Centaur combination.