Blue Origin developed the BE-4 engines used by United Launch Alliance’s Vulcan Centaur rocket.
The BE-4 is a staged-combustion rocket engine that burns liquefied natural gas, primarily methane, with liquid oxygen. ULA selected it to replace the Russian RD-180 engines previously used on the Atlas V first stage.
The same engine is intended to power the first stage of Blue Origin’s New Glenn rocket. This makes the BE-4 an important connection between two commercial launch programs, even though Blue Origin and ULA operate different rockets.
The BE-4 is sometimes incorrectly attributed to SpaceX because SpaceX also uses methane-fueled engines. SpaceX’s Raptor family powers Starship and Super Heavy, while BE-4 is a Blue Origin design supplied to ULA.