Paul Rand
Saul Bass
Peter Saville
Josef Muller-Brockmann
Massimo Vignelli
Milton Glaser
Michael Beirut
Paula Scher
More current and not quite on par with those above just yet:
Jessica Hische
Dan Draplin
Frank Chimero
Not graphic design per se but still applicable:
Dieter Rams
As others mentioned, you’ll need a strong typographic foundation. A book called “Thinking With Type” by Ellen Lupton is a good start.
Feel free to message me with any other questions.