SMG4 - The creator of the bloopers and one of the two protagonists of the series. He resides in Peach's Castle with Mario, often making his bloopers (or playing Minecraft), and gets generally annoyed by Mario (who is apparently his assistant), but he likes him nonetheless.
Mario - The other protagonist and central character of the series. He is crazy for spaghetti and incredibly retarded. Almost all of the bloopers revolve around him and the trouble that he gets the main cast and himself into.
Luigi - Mario's younger brother and the deuteragonist of the series. He makes smarter decisions than Mario, but he's still as cowardly as he is in the actual games, if not more so.
Bowser - Originally the main antagonist (partnered and then replaced by SMG3) of the series, who was always trying to kidnap Princess Peach. Despite them canonically being archenemies, here he is actually one of Mario's friends. He isn't as smart as his Nintendo counterpart and commonly falls victim to his own incompetence. He been mostly seen being absent during The Anime Arc but reappeared between late 2019 and mid-2020. Then he slightly decreased again in The YouTube Arc limited into minor roles.
Bob Bobowski - A Garo who evidently was a sewer wizard from The Legend of Zelda: Majora's Mask. Mario and Luigi first met him in SM64 Bloopers: Can Ganondorf come out to play?. He's obsessed with fame, money, and getting the most screen-time in his appearances. Despite his humorous punching bag status, Bob has proven he can be a downright repulsive, self-admitted bastard if he isn't given the attention he wants, especially since he is the primary antagonist of The Rapper Bob Arc.
Meggy Spletzer - Formerly a female Inkling transformed into a human who was accidentally captured in a paint bucket, causing her to be freed and flee into a manhole that leads to Inkopolis, taking Mario along with her. She completes in Turf War tournaments with her team, the Splat Squad. After the events of SMG4 Movie: Meggy's Destiny, she fulfilled her dream becoming a Splatfest champion, and later moved to the Mushroom Kingdom and intends to have a career of crime-fighting.
Saiko Bichitaru - A beautiful but insane love interest from an unnamed dating simulator game based on Doki Doki Literature Club. Boopkins brought her to life one day with Kamek's wand in order for him to have a real girlfriend. Due to her being mentally unstable for wanting attention, their relationship ends in tragedy. However, she has since recovered from the said incident and has considered Boopkins a friend, though she remains a psychopath.
Tari - A shy blue-haired gamer who tends to get hurt a lot. Mario turns to her for guidance on how to be a good player and kick SMG4's butt at Super Smash Each Other In The Ass Bros, and as such became friends with them both and the rest of the gang, namely Meggy and Saiko.
Axol - An Inkopolis-born manga artist from Japan who can create anime characters using his special pen, the Inkweaver.
Starman3 - A former friend and ally of SMG4. Due to real-life controversies, he has been removed from SMG4's videos.
Peach Toadstool - The ruler of the Mushroom Kingdom and the castle Mario and almost everyone else resides in. She was the prominent female character in early bloopers until Meggy took over that role in late 2017, hence explaining her recent lack of appearances. She has had antagonistic appearances in recent years, such as in Part 1 of The Anime Arc (alongside Desti) and SMG4: Food Wars, however, she is still often acting a nagging motherly-figure to the gang.
Steve - The default avatar used in the world of Minecraft but a character in the SMG4 universe. He's usually friendly with the rest of the members although insulting Minecraft in any way will result in getting on his bad side. He served as a major recurring character in earlier bloopers but stopped appearing with the crew as of Season 8. After that, he mostly appears in Minecraft-themed bloopers such as SMG4: If Mario Was in... Minecraft and SMG4: The Minecraft Plague.
Chris Gordman - One of the main protagonists of Guards N' Retards along with his partner Swagmaster69696969696 who used to work as guards at Fresh Spaghetti Tubbie. He's much more competent and sane than Swag is. Despite Chris and Swagmaster allied with the SMG4 crew briefly after. He and Swagmaster69696969696 have been tertiary antagonists in the The Anime Arc previously.
Yoshi - A green dinosaur who acts as an ally of the Mario Bros. He is usually depicted as a fruit lover, wallet thief, drug user, weapons dealer, and even a tax fraud criminal in the series. His personality seems to wildly vary with every episode he shows up in.
Professor E. Gadd - One of the main characters of Luigi's Mansion and its sequel. He started off as a small character in early videos but has become a recurring character as of 2014. He played a major role in SMG4 Movie: Meggy's Destiny.
Jeeves - A sentient fork who owns several companies.
Joe Boopkins - Fishy Boopkins's and JubJub Boopkin's father. He's basically a giant version of Octodad with Cthulhu's head.
Sonic the Hedgehog - A super-fast Mobian hedgehog and the main protagonist of his namesake series. He briefly helped Bowser stopped Princess Peach from being engaged by Dr. Eggman in Egg and Peach. He is also the current "waifu" (romantic interest) of Swagmaster.
SMG3 - SMG4's arch-nemesis and doppelganger and the overall main antagonist of the series and The YouTube Arc. He mainly wants to kill SMG4 and his friends and take over the world, though on some occasions he isn't as harmful as he seems. He is currently seen being the only enemy who actively antagonizes the gang.
Wario - Mario's greedy fat boi arch-rival who starred in "The Wacky Wario Bros." episodes for a while alongside Waluigi. He loves money.
Waluigi - Wario's partner/brother. Also the arch-rival of Luigi who starred in "The Wacky Wario Bros." episodes alongside Wario. After harnessing the power of rejection, he became the main antagonist of The Waluigi Arc.
Francis - An anime-obsessed chameleon originating from the game Super Paper Mario and the primary antagonist of Part 2 of The Anime Arc, as well as the main antagonist of the arc overall.
Anime Secret Service (formerly) - Princess Peach's anime prevention force. They are the Anime Cartel's rival. Despite being officially disbanded since SMG4: Mario Saves Anime, they help SMG4's Gang fight Francis and the Anime Cartel.
Team Killer Ink - A team of Inklings competing in the final Splatfest event who are racist towards humans. They served as the primary antagonists of the computer-animated film Meggy's Destiny.
Many SM64 Machinimist characters like MM, MCG, AustinDawgyDawg, GageDawg, and Pinkolol16, were unconfirmed or presumed to be official members of the main cast due to them being absent in recent Seasons, even in minor cameo appearances.
Swagmaster and Chris became more prominent recurring characters outside their own series since it eventually merged with the main SMG4 series in 2019 and often times allied with the gang.
Comparisons can be made between them and any team of protagonists, albeit as of late, comparisons to both DC Comics' Justice League and Marvel Comics Avengers have been more prevalent, especially with memes involving Avengers: Infinity War and Endgame throughout 2018 and 2019.
Out of all the members in the gang, only Mario and Bowser are known to be part of two gangs, the other being SMG3's Gang, with Bowser being a member even before he defected to SMG4's Gang.