It would be hard to argue with anyone who referred to Jack Kirby as the greatest comic book artist of all-time. He had unquestionable influence on the history of comics and contributed a massive amount of work. His work spans decades of comics, starting all the way back in the Golden Age. He helped create almost every major Marvel super hero, including the Fantastic Four, the Incredible Hulk, Iron Man, the X-Men, and the Silver Surfer. Even after his run revolutionizing comics in the 60’s, he went on to DC and created the Fourth World Saga, a sprawling space opera that encompassed numerous titles.
Gary Groth conducted an fairly complete retrospective interview with Jack Kirby a few years before he died. It is a long read, but worth it, because it takes you through Kirby’s entire life, which spanned all those decades of comic history. It also is a bit controversial because Kirby in large part dismisses Stan Lee’s contribution to the creation of most of the Marvel comics they worked on together.
If you don’t want to read, there is a nice documentary entitled Jack Kirby: Story Teller (currently available in five parts on YouTube).
For more info on Jack Kirby there is the Jack Kirby Museum, which includes a large amount of information on Kirby.