The exact origins of poker are very obscure and speculative. Historians are still unable to agree exactly where poker came from, how the game came to be called poker, or who invented it. It is, however, very likely that this great card game was first played with a deck consisting of only 20 playing cards, the four 10s, Jacks, Queens, Kings and Aces.
Another detail that is almost certain is that poker was first mentioned in print, in 1834, in a book entitled An Exposure of the Arts and Miseries of Gambling, written by Jonathan H. Green. Green has often been misquoted for having called poker "the cheating game." This is, however, incorrect. Although Green did expose many of the poker scams of the time, he never actually called it "the cheating game" with these exact words. But he does make it clear that in his days poker was more or less a card game that was used as a swindle, to rid the suckers of their money. This is the aspect of this card game that is most interesting to us.
Many things have changed since Jonathan Green's infamous book, written in the 19th century. Poker players have developed rules that have become generally adopted throughout the world (basic poker rules won't be discussed here, but you are welcome to visit the general rules of card games page on our sister site Playing Cards Online, for detailed info). Also, as we all know, poker has spread throughout the virtual world of online gambling and many poker sites have been born to satisfy the needs of millions of poker players throughout the world. Online poker has become a big business. Entire networks have been built to promote and list all the poker sites (which have now become household names). These sites have become popular through massive ad networks and cross-promotion through thousands of gambling sites. If you do a quick Google search for "poker listings" you should not have too much trouble finding the sites that promote online poker rooms.
Since undisputable historic evidence supporting any of the theories of the early origins of poker does not exist, we have to accept that fact that we will probably never know for sure where poker originated, and how. We can simply take accept this fact and move on to the more recent, and documented, history of this card game. Gamblers never think to record history, they just put some money in the pot and hope to win. This is still the case today, but at least we have some documented records that we can go by.
One infamous gambler that we should not forget to mention was George Devol, frontier gambler and cardsharp, and author of the classic gambling book Forty Years a Gambler on the Mississippi. This is yet another book that makes it pretty clear that poker was a crooked game. There are also some other books of interest to historians, to support the theory that poker has always been crooked. Some of the better known books are Sharps and Flats, and The Mott Street Poker Club.
So, when it comes to the early origins of poker, all one can really hope to find are (pseudo) theories and speculations. We can either accept the fact that we'll probably never know where poker came from or we can simply pick a theory that sounds good and choose to believe it.

Also, please check the following blog posts for further articles about poker.
The Basic Principle of Poker Cheating