As with locating the source of many different things, there is some disagreement about the origins of the game of poker. It probably depends on what exactly you view as similar enough to the current versions to be seriously regarded as a forerunner.
The German game of Pochspiel is possibly the earliest recorded similar game and can be
dated to at least 1441. Variations on this name include the German word Pochen, the French Poque and the Irish word Poka, all meaning pocket. The current name is almost certainly derived from the Irish from. Pochspiel was, as stated though, the earliest recorded version to feature betting, bluffing and hand rankings.
A Persian game called As Nas has also been cited as a predecessor of Poker which certainly does resemble the modern version but again, historians disagree on how much credit it should be given.
This does not mean that there is any relation between these original games and the modern form however and a French game called Brelan is commonly regarded as having a direct ancestry. The English game of Brag is known to be a direct descendent of Brelan and Brag incorporates bluffing as an integral part of the game.
Many do believe however, that all talk of ancient ancestries is irrelevant and that the history of Poker really only dates back to the Mississippi region of the American South in the mid-nineteenth century. This belief is based on the usage in Poker of a very specific system of betting used in this region and still used now. It was unknown in any previous games. The game (and other forms of gambling) took place historically on large riverboats on the Mississippi river to avoid the illegality of gambling on shore. The boats gradually spread this form of the game North and its popularity increased accordingly.
In recent years, Poker has become dramatically more popular, largely due to easy access
to online gambling and televised tournaments.