Very sad news regarding Spain Rodriguez's passing. I discovered his work through reference books about comics (most probably Toutain's Historia de los Comics), at an age in which I wasn't supposed to read underground comics. Nevertheless, being a big fan of Harvey Kurtzman's MAD, it wasn't a big surprise that I ended up being an enthusiastic reader of underground comics as well, most definitely including Spain Rodriguez's work.
I was able to track down Spain's work thanks to Fantagraphics' reprint volumes (part of their quixotic attempt to reprint the work of several underground comix artists during a period in which there wasn't a bookstore market for comics like these): 1989's Trashman Lives! and 1994's My True Story, a book that collected his autobiographical and non-fiction stories, a body of work that probably showed Spain at his best.
The following is just a minor footnote in his career, but it is a somewhat unexpected example of Spain's influence and may be of interest for those who (like me) enjoy comics trivia.
A few months ago comics writer Pat Mills started posting on his blog a series of articles about the creation of Judge Dredd. Back in September he wrote the following: