With his work, Pekar paved the way for a whole new type of naturalistic, autobiographical comics. Without him, comics by artists like Joe Sacco, Marjane Satrapi, and Joe Matt would probably be completely different. I interviewed Pekar at Town Hall in April of 2006 (the Seattle Channel has this interview somewhere in their archives) and I'm delighted to say that he was exactly what he put on the page: A grumpy guy with great aesthetic taste, a passion for art, and a very, very low tolerance for bullshit.
If you'd like to try Pekar's comics, you should start with either the Best Of edition that came out for the movie or Bob & Harv's Comics. Pekar and Robert Crumb really brought out the best in each other* when they collaborated.
I hate that I live in a world that will never see another new American Splendor comic. Rest in peace, Harvey.
* In superhero comics nerd-speak, the Pekar-Crumb collaborations are the Byrne/Claremont X-Men run of the indie comics world**.
** I'm probably going to some kind of comics hell for writing that sentence.