In Street Fighter Alpha 3, he says the following:

"I hate the Art of Fighting, but I wanna be the King of Fighters" implying that he wants to be The King of Fighters™ despite hating the Art of Fighting™

Dan used to train with Ryu and Ken Masters' master, but he was kicked out of the group chat after his master realized he was purely training to get his sweet revenge against Sagat. After that, Dan then created his own fighting art

He has defeated Sagat in Street Fighter Alpha, taking revenge on the murderer of his father, Go Hibiki, who Sagat lost one of his eyes for. Sagat in fact went all out on his battle against the almighty Dan, but his techniques were nothing compared to that of the Strongest, thus leading to his defeat

He has also taught Sakura many of the things he knew, as well as administrating his own dojo for those who wanted to know about the strength of The Strongest, and went to (almost) the rest of the tournaments, looking forward to promote his dojo to other people.

In gameplay, he has by far the most useful and viable moveset, but he's also very broken, so due to that he's banned in all of the games he appears in, hence why no-one uses him.

His moveset usually consists of moves inspired on Ryo Sakazaki's and Robert Garcia's, both characters from the Art of Fighting videogame series by SNK, he does a mockery to their moves by highly improving them, making them more useful than the base games has ever made them be.

He has also mastered the Art of Taunting™, a forgotten art that only almighty ones can master, an ability so forgotten than in all of the 3 Street Fighter Alpha games, only he can perform taunts more than once per round. He can taunt while rolling, jumping and even perform his most powerful technique that consists of a legendary taunt, mocking his enemies to oblivion and instantly defeating them in the process. In Street Fighter V, it's at the cost of making him extremely vulnerable to more damage. In other games, his Legendary Taunt gives his opponent more super meter (which is actually a reference to how taunts work in Art of Fighting, but quite the opposite to it) and gets his own back after finishing the taunt.

--- Other Fun Facts

Dan is somehow friends with Blanka, who first appeared in Street Fighter 2.

In his debut game, Street Fighter Alpha (1), his sprite made him look more like Robert Garcia, previously mentioned for being one of the inspirations to make this character. He is also a secret character in there, only accesible by holding start and performing an input on the select character menu while selecting the random option. The command is the following:

"Start (Hold) while selecting Random, rapidly press LP, LK, K, HK, HP, P simultaneously)

Outside of the Alpha series, Dan would appear in Marvel Super Heroes vs. Street Fighter, Marvel vs. Capcom 2, SNK vs. Capcom: The Match of The Millenium (and Chaos), Capcom vs. SNK 1 (and 2), Super Gem Fighter Mini Mix, in Street Fighter x Tekken (as your master), and finally, Street Fighter IV and V.