Mercedes was the name of the daughter of a racer who drove early DMG cars (Daimler Motoren Gesellschaft). The brand name Mercedes-Benz was owned by the production company Daimler-Benz, which was formed when DMG merged with Benz & Cie.
I knew the Mercedes name was from someone's daughter, but had to look up that said someone, and the full history of how the name "Mercedes-Benz" came to be.