It should be noted that his explanation for the photoelectric proved that photons we’re discrete objects, paving the way for quantum mechanics, and his explanation for Brownian motion was the first definitive proof that matter was made up of atoms.
I point this out just because someone unfamiliar with these topics might think that those two papers were some esoteric things that physicists appreciate but most people wouldn’t.
Einstein always gets associated with relativity and e=mc^2, but I’d argue those were not his top accomplishments. The Nobel Prize committee seemed to agree. (He won for his work on the photoelectric effect i.e. quantum mechanics.)