Gamblers follows a card (or dice) theme, uses cards, dice, darts, coins and gambling implements as weapons, and is very well-versed in blackjack, poker, craps, slots, and all sorts of casino games. They rely much more on luck and cunning than on skill or outright power, and very seldom take it too hard on the occasions they lose, usually due to believing it was due to chance.
They tend to be slick, either elegant or gaudy, just like professional card players from the past, and are more towards lean and nimble than strong and resistant. Due to their very nature, they tend to fit the definition of tricksters, and one would be hard-pressed to find a particularly slow-witted person, or a grunt, in the position of the Gambler.
The entire theme around the gambler makes him usually either an Anti-Hero or an Anti-Villain, due to a view that they usually revere luck and chance over pledged allegiances, and that they will usually be too chaotic to be too specifically good or evil, with The Joker being a rather brutal exception to this rule. This trope is almost entirely populated by men, and it has been increasingly common as time goes by. See also: Death Dealer (using playing cards as weapons), as well as Born Lucky and Winds of Destiny, Change (when the character has actual powers over luck).
In a video game, expect them to have Randomized Damage Attacks as part of their "luck" gimmick.