Marcus Damon, known in the Japanese version as Masaru Daimon (大門 大 Daimon Masaru?) (his name is probably also an intended pun as it could be read Daimon Dai while daimondai means "big problem", which would make sense given his love for fighting), is a fictional character in the Digimon Data Squad series. He is the first lead character of any Digimon series (anime as well as manga) that doesn't wear goggles. Marcus is also the first to hurt a digimon on a regular basis. He also appears in quests of the game Digimon World D.S. and Digimon World: Dawn and Dusk and is the main playable character in Digimon World Data Squad.
Marcus is a fourteen-year-old student who loves to fight and, in a way, considers himself to be an "ultimate fighter" ("street fighter" in the original Japanese version). He lives with his mother Sarah (Sayuri) and younger sister Kristy (Chika). Marcus meets and fights Agumon in the first episode of the series. When the fight ends in a draw, Agumon agrees to become his partner. Soon afterwards he's recruited as a member of D.A.T.S. As Marcus's partner, Agumon idolizes him and refers to him as his "aniki" (兄貴, a Japanese colloquialism for "older brother", used in this case with the connotation of "boss" as seen in the Yakuza). Marcus is one of the few shown to fight Digimon by himself, though he still counts on Agumon's help to fight the stronger opponents. Even though others can evoke their DNA charges by themselves, Marcus must connect a punch on an enemy to do so, subsequently using it to digivolve Agumon.
Before leaving the Human World to confront Merukimon (Mercurymon), Marcus gained an alternate motive for going: to find his father Spencer (Suguru) who he believes to still be alive and bring him back home. However, the only clue he has about his whereabouts was given by Merukimon himself, who revealed to be a friend of Spencer and said he set off in search for Yggdrasil, the god of the Digital World in his effort to build a coexistence between humans and digimon. Marcus only learned anything else about Spencer when he and his friends reached ElDradimon (ElDoradimon) and learned that the people there has a debt of gratitude with him for helping the city years ago. They swore to protect the city from Kurata's army, but in the end there was little they could do to prevent ElDradimon from being destroyed.
Another moment of despair occurred when Thomas, for personal reasons was forced to side with Kurata and he had to fight him. During the battle between ShineGreymon and MirageGaogamon, Like Tai Kamiya and Takato Matsuki, Marcus's anger triggered the dark digisoul inside himself, dark digivolving his partner to a corrupt and rampaging version of ShineGreymon Burst Mode called ShineGreymon Ruin Mode. After finally stopping him, he returned to a digi-egg state, but did not take long for Agumon to return to life and digivolve to ShineGreymon once more. Imbued by the determination to protect those that he loved dearly: his friends, his fellow DATS members who were close friends akin to family and of course his family themselves, Marcus was able to bring him properly to ShineGreymon Burst Mode this time to fight Belphemon. After Belphemon's defeat the DATS team face a threat even greater when King Drasil/(Yggdrasil), the god of the Digital World, decides to wipe out the Human World to end the struggle between the worlds once and for all, with the help of the Royal Knights. Marcus confronts Yggdrasil himself, just to discover that he is in fact Spencer Damon, his long lost father. After being rescued by Sleipmon, Marcus intends to go back to the Digital World to confront his father.
After meeting up with Gotsumon again, Marcus and Agumon faced off against Craniamon (Craniummon) once more, where the GeoGrey Sword actually broke. With help from the others, they were permitted to see King Drasil. Upon reaching him, Marcus fought his father, but couldn't land a hit. However, after hearing his father's disembodied voice, and with help from the Digimon, Marcus was able to connect a hit. BanchoLeomon (BantyoLeomon) appeared to help Marcus, only to reveal that he was holding the real Spencer inside his body before grabbing Yggdrasil and telling Marcus to kill them both. With severe hesitation, Marcus ordered ShineGreymon to unleash the attack that took them out. Just before the attack hits, BanchoLeomon and Spencer both thank Marcus. With King Drasil seemingly defeated, and the World Tree destroyed, everything seems like it's over. However, King Drasil's true form appears and it took a hit from Marcus to convince it not to continue and rest to see the results of a humam/Digimon co-existence, reviving Spencer. In the series epilogue, Marcus decides to stay in the Digital World and help Agumon keep the riff raff in line and out of trouble.
- According to the first episode, his birthday is the same day as the day Digimon Savers started in Japan, April 2.
- In the Japanese version, when referring to himself, Masaru adds -sama onto his name, which in Japan, shows great arrogance.