The basic reason for why Stu Ungar changed from gin rummy to poker was that Stu was a bit too skilled at it. So good was he, that no player was able equal him. Even the so-called champions who were supposed to be the best at gin rummy were demolished when they played with Mr. Ungar. One such gin masters was Harry Stein, nicknamed, "Yonkie". Harry Stein was handed such a debilitating defeat at the hands of mr. ungar that he apparently quit playing it as a pro and never resurfaced at a gin tournament.
Of course, with a distinction like that it was not long before gamblers became afraid of gambling against stu. He couldn’t find any games and in his agony he started doing something no one had done prior. He presented beginning handicaps to potential competitors with the hope that they might just play against him if they thought they had an advantage. He deliberately started from a disadvantageous arrangement and one account has it that he even competed with a consistent bad egg. During the game, he received a few words of wisdom that the cheater was at it once again but Stu Ungar guaranteed that he knew of the dishonestly and he would still actually win, which he did, of course.
The same trend followed Stu Ungar into Las Vegas. He won so often that the casinos began requesting that he not to play in their rooms anymore. The reason was that other casino customers refused to sit at the poker table if Stu was playing.
Stu Ungar is remembered more for his achievements in texas holdem poker but he himself always maintained that he was much more skilled at gin rummy.
He defeated Doyle Brunson in the World Series of Poker in 1980 and became the youngest world champion. Due to his features that made him seem far younger than he was, he got the nickname, "The Kid".