The origins of the comic book are somewhat controversial and perhaps the jury is still out. So lets go back to the cartoonish broadsheets of the Middle Ages, which were parchment products, created by anonymous woodcutters. As mass circulation of these broadsheets became possible, they soon developed a market, particularly at public executions, popular events for centuries (ugh), which drew thousands of happy spectators. Many of these spectators would invest in an artist's rendering of a hanging or burning, and thus making a very lucky day for the broadsheet seller.
The broadsheet evolved into higher-level content as humor was introduced. Eventually, all types of broadsheets emerged, which were eventually bound in collections, the prototype of the modern magazine. Magazines formatted like the popular Punch, an elegant British creation, became the primary focus of documentary accounts of news and events, fiction and humor. One can see in Punch, the sophisticated evolution of a comic style, particularly in respect of the evolution of comics in Great Britain. Still and all, from an historical standpoint, the comic strip stood in the alley, waiting to be born. And then some say Great Britain's Ally Sloper's "Half Alley" was the first comic-book. This was a black and white tabloid that had panels of cartoons mixed with a sliver of news; circa 1884.
Now while all this was going on in Great Britain, the United States had its own brand of evolution. Instead of magazines, US newspapers took the lead in creating the comic book industry. Newspapers, with their first steps, took their single image gags and evolved them into multi-paneled comic strips. It was during this period that William Randolph Hearst scored a knockout with the Yellow Kid, which was actually printed in yellow ink.
So where did the actual comic book begin? Some say it was with reprints of Carl Schultz' Foxy Grandpa, from 1901 to 1905. Although others say it was Great Britain's Ally Sloper's Half Alley. In 1902, Hearst published the Katzenjammer Kids and Happy Hooligan in books with cardboard covers. For a time, the Yellow Kid himself was a top contender. But it depends how rigid you are in your description of a comic-book. These examples, for sure, were predecessors to the modern comic-book, which exploded in the 1930's.
The Whitman Publishing Company, in 1934, became one of the pre-launchers for the modern comic book. They published forty issues of Famous Comics, which was a black and white hardcover reprint. The first regularly published comic in the more recognizable modern format though, was Famous Funnies. It featured such memorable characters as Joe Palooka, Buck Rogers and Mutt and Jeff.
Superheroes as we know them today took a strong foothold in the 1930's. In 1938, Max C. Gaines, who was one of the comic industry giants, brought "Superman" to Dell Comics publisher, Harry Donenfield. Donenfield scored the comic coup of the century when he published a story written by two teenagers, Jerry Siegel and Joe Shuster- and so "Superman of Metropolis" (the title of their short story they wrote in their own fanzine) was born. Superman was to set a standard for comic book heroes that persist to this day.