Ryuhaku Todoh. Despite only appearing in the very first game (with a single special move!), he has a large number of cameo appearances under his belt and was eventually added to the roster of Capcom vs. SNK 2: Mark of the Millennium. He also had his daughter Kasumi—herself an example of this trope—to pick up the slack for the Todoh family in the third game and The King of Fighters.
Eiji Kisaragi from 2. When he returned to KOF in XI (after a hiatus spanning eight games and several cameos in the backgrounds of said games), the fandom went bonkers.
Germans Love David Hasselhoff: Jin Fu-Ha from 3 is quite popular among the Japanese fanbase, who have been clamoring for him to make it into a KOF game (perhaps the reason behind his cameo in XII?); elsewhere... wait, who are we talking about again? Oh yeah, the nondescript musclebound ninja whose spinning lariat special move is turned into a mini-version of an amusement park ride for children in the background of a KOF 2002: Unlimited Match stage.
Good Bad Bugs: In at least some arcade versions of Art of Fighting 2, it was possible to win a match by making a lock on your opponent followed by hitting him with a Ko'ou Ken or equivalent special attack just when they are getting up from the floor. note This may not to work with all characters, though. That move would stun the opponent allowing you to give them another lock. Lather, rinse, and repeat.
Ryo is often mocked as a "Ryu clone", yet his upper and lower body parries which he's had since AOF3 have now become Ryu's V-Skill in Street Fighter V. And Ryu's Shinku Hadoken becomes closer in appearance to Ryo's Haoh Sho Koh Ken with each iteration.
Likewise, Robert was seen as SNK's answer to Ken. Yet, years later, Capcom started borrowing aspects of Robert's character. Such as giving Ken a ponytail (starting in the Alpha series), adapting Robert's propensity for kicks, even lifting Robert's backstory verbatim as Ken's note i.e. that both come from billionaire families and were sent to train at their respective schools by their fathers.
The US version of Art of Fighting 2 redubs some of Robert's, King's and John's lines with English-speaking actors, and Mr. Big and Geese are voiced in English in either version. The problem is, nobody can act or kiai worth a damn. "Ha-HA! Piece of... cake!"
Sequelitis: Art of Fighting 3 is generally considered to be the weakest entry in the series, with many critics citing the poor balance as a major problem.
Visual Effects of Awesome: Art of Fighting 3 is easily one of the most graphically impressive fighting games ever made. The character animations are amazingly smooth (since they were made via Rotoscoping), the background art is immensely detailed, and it features both sprite scaling and parallax scrolling at the same time. Did we mention this game came out in 1996?
Woolseyism: The English translation of the second game was almost a Gag Translation, changing the serious tone of most endings into jokes, which are arguably much more enjoyable than the originals. Curiously, the Spanish-translated version of the game retains the serious tone of the original Japanese dialogue.