Although K9999 does not appear in The King of Fighters Neowave, his data remains in the arcade version and can be selected using external cheat devices. Here, he uses Kyo's icon on the select screen and Kula's icon while in battle. In battle, his color palette is bugged, but is otherwise fully functional.
All of his move names are quotes taken from the movie Akira, as well as mimicking several iconic stills from the said movie in his attack motions.
One of K9999's Super Special Moves in KOF 2001 and KOF 2002 was him morphing his hand into a gun. In the American and European releases of those games, his gun arm was censored and changed to just his fist and the explosions.
K9999 is one of the very few characters in fighting game history (and in the KOF/SNK series') to not have his cr. or a crouching strongest normal as his standard sweep; his cr. acts as one instead.
In a 2005 poll made by SNK Playmore USA, he was voted as the seventh fan favorite character with a total of 156 votes.
K9999 is the only character of the series with updated versions released in future games.
K9999, Nameless and Krohnen share the same blood type, likely stemming from Kyo Kusanagi's blood.
However, only Nameless has the RH factor (negative) present in Kyo's blood.
K9999 and Krohnen also share the same type of favorite food (peanuts and nuts are part of a same family [nuts]).
Some informations in The King of Fighters XV confirms that Krohnen and K9999 are the same person:
His special intro against Kusanagi is yet another direct homage of the anime film Akira. Kusanagi's voice actor before KOF Sky Stage, Mitsuo Iwata, also voiced the character Shōtarō Kaneda, Tetsuo's nemesis and prior best friend. This is referenced again in The King of Fighters XV, when Krohnen (the recent update version of the character) confronts Kyo Kusanagi (a character that Kusanagi was created and based on) in the Story Mode.
One of Krohnen's generic victory quotes has him saying "Were you excepting me to be more hot-headed? Well, unfortunately for you, I've changed.", further suggesting that he is indeed K9999.
As the leader of the Krohnen Team (officially named as Team Krohnen), he has Ángel and, ironically, Kula under his wing. Ángel as a member makes sense and strengthens his identity as K9999, as the two are friends and look out for one another. However, Kula is a perceived enemy, basing on his prior interaction as K9999 in KOF 2001, with the latter joining the team in protest against K' (he and Kula had a grudge), when they took her as a "kidnapped hostage." Kula, as per their team story, however, has no intention of escaping her "captors."
The Team Story of Team Krohnen (released shortly after the team's confirmation) reaffirms this information.
Krohnen is wary against surveillance from remnants of NESTS, confirming he did defect from the cartel.
Krohnen relies on Ángel for errands and the two are constantly on the run and changing locations. Moreover, K9999 was stated to consider Ángel as the one he considers a friend and, by implication, the only person he trusts.
Krohnen is stated to be using aliases to evade surveillance.
His hostility towards K' and Kusanagi (and by extension, their DNA precursor, Kyo Kusanagi) is a trait well known to K9999 as well. However, while Kula is considered an enemy as well by association, Krohnen is surprisingly tolerant of her, teaming up with the child two times (three if counting KOF 2002).
In their team ending, Ángel refers to Krohnen by his old name, K9999, telling him he has matured.
His updated version's first name (Krohnen) bears similarities to the German word "krone", which means "crown".
Krohnen's Japanese Katakana's spelling is a play off the word "Clone", with the difference of only one character place in it (Krohnen = クローネン/Clone = クローン).
Krohnen's name also could be a reference to Canadian film director David Cronenberg, one of the principal originators of what is commonly known as the body horror genre, with his films exploring visceral bodily transformation, infection, technology and the intertwining of the psychological with the physical. Curiously, K9999, Krohnen and Nameless show these features in their moves.
His updated version's last name, "McDougall" was not present on in-game nor both of his character and team bios, making him having similar situation as Kim Kaphwan in the Maximum Impact series and starting from The King of Fighters Neowave (unless if counting Leona's surname [Heidern]).
Krohnen's surname is possibly a reference to Kane McDougall, protagonist of Blue Knight Beserga Story, a spin-off of the mecha anime series Armored Trooper Votoms. The spin-off also inspired K' and Maxima's names (as a Kane's clone and the robot ATM-FX1 Zerberus VR-Maxima, respectively).
or a crouching strongest normal as his standard sweep; his cr.
acts as one instead.