Through the history of the US space program there have been 2 corporations which made most of the rocket engines for the boosters Aerojet and Rocketdyne. Up until 10 years ago it was hard to find a space mission they hadn't provided hardware for. Nowadays it's hard to find a rocket booster which uses their engines.
AerojetRocketdyne was created in 2013 out of a merger of these and over the weekend it was announced that Lockheed Martin is buying this historic company.
So I figured it'd be worth talking about these organizations and how important they've been to the space program in the past, and how they may be losing out in the booster market but still keep providing space hardware for other niches.

History of Aerojet Rocketdyne from their own site:
https://www.rocket.com/whoweare/his...

Here's a list of US rocket engines with their manufacturers:
http://www.b14643.de/Spacerockets/Spe...