The rocket engine that powered the first stage of SpaceX’s Falcon 9 was Merlin.
Falcon 9 first stages use Merlin engines designed and built by SpaceX. The engine burns rocket-grade kerosene, called RP-1, with liquid oxygen. Early Falcon 9 versions used nine Merlin 1C engines, while later versions introduced the more powerful Merlin 1D and Merlin 1D Vacuum variants for different stages and missions.
The standard Falcon 9 first stage uses a cluster of nine sea-level Merlin engines. Clustering provides substantial thrust while allowing the vehicle to continue operating if an engine shuts down under some flight conditions. The first stage can also reignite for controlled descent and landing, a key part of Falcon 9’s reusability.
Merlin is not the engine family used by SpaceX’s newer Starship vehicle; Starship uses methane-fueled Raptor engines. NASA’s Space Shuttle used RS-25 engines, another distinct design.