Dumbledore (full name Albus Dumbledore) is the principal of the wizard academy Hogwarts in the Harry Potter series. In SuperMarioGlitchy4's videos, he appears especially in the blooper "Super Mario 64 Bloopers: Spells n' Wiztards", in which he's the principal of Hobowarts, a parody of Hogwarts.
Dumbledore is a rather tall old man; he has long white hair and beard, and a white mustache. He wears half-moon glasses which often have a pink reflection. He also wears a brown wizard dress with very long and wide sleeves and a hat which is brown like the dress. Outside of SMG4's bloopers, he doesn't always wear those same clothes.
In the original series, Dumbledore is a discreet person. However, in SMG4's videos, he seems to be a bit more crazy and energetic than in the series, as several other characters in SMG4's bloopers. He also tends to scream his name when he appears.
Dumbledore was first mentioned by SMG4 when the latter was talking to a Minecraftian old man (that was possibly a nickname or him) in the blooper "Super Mario 64 Bloopers: Befriend the End" released on 2012. Later on 2014, Dumbledore made his first canonical appearance in "Super Mario 64 Bloopers: Spells n' Wiztards" which is his most prominent one. In this video, he's the principal of the wizard academy Hobowarts which is inspired by Hogwarts in the Harry Potter series. He welcomes Mario and SMG4 at that academy and assigns them to the "Team Mushroomdors" of Hobowarts. He later reappears in the same blooper and holds a spell competition in which Bowser (who plays in the Team Slytherbastards) even creates a clone of Dumbledore when he tries to summon a garden gnome.
About one week later, Dumbledore makes a cameo reappearance in "Ssenmodnar 8 (150k Special)", in the 10th and last skit of the blooper, in which Dr. Eggman slapped his butt for amusement. Then Dumbledore turns towards him and says "HEY, WHAT THE F**K!" as Robotnik runs away while laughing. After this, the part with all the cutscenes then turns out to be a dream that Mario made when he was trapped into a Giant Ugly Floating Mario Head who is the main character of the video.
At the end of the year, Dumbledore makes a brief cameo in "The Retardness of 2014" (a blooper specially made to close 2014), in a clip from "Spells n' Wiztards" when Mario and SMG4 go over the year one last time. That scene features him revealing his own (last) name to Mario and SMG4 when he welcomes them at Hobowarts.
He later reappears as a cameo on 2015 in "Super Happy Fun Fun Gameshow".