Wilford Warfstache is Mark's most widely known alter ego, characterized by his pink flowing moustache and amusing deep voice. He became somewhat of an icon of Mark's channel shortly after the release of The Fall of Slender Man. Since the sketch comedy's release, he has often been associated with the act of seeking answers from the Slender Man about his personal life.
A lesser-known alter ego, Mark-Bot is simply a robotized version of Mark, speaking in the typical monotone/tri-tone, repeating words and using hand gestures often associated with the Robot Dance. Mark-Bot has only made minor appearances in a few of Mark's videos, but is featured more prominently in his early livestreams, such as his Tekkit For Two livestream.
Darkiplier is similar to Markiplier, but depicted as a being with a much darker attitude, hence the namesake. He could be seen as Markiplier's opposite, displaying behaviour that highly contrasts Mark's more upbeat and happy personality. Darkiplier came to be known after Mark's displays of creepiness towards the viewers throughout some of his videos. At the time,"Darkiplier" merely referred to Mark's creepy side, but the fanbase soon interpreted Darkiplier as a separate personality. Examples of Darkiplier can be found in videos such as Error #53 and Mr. Kitty Saves The World.
Mark's interpretation of Santa Claus is significantly different to the well-known jolly man, bearing a more disturbing personality, behaving more harshly towards his elves and being a heavy drinker of "eggnog". Santa grew to fame within the fanbase after the release of Mark's Happy Wheels Highlights series.
The Ham-Fisted Avenger
The Ham-Fisted Avenger is another minor alter-ego only seen during the Slaps-Giving livestreams in November of 2012. Against his arch-rival Sissy-Slapping Sue (Wade), The Ham-Fisted Avenger has been shown as the superior of the two slappers, but both seem to hold an even chance against each other as both show the same amount of pain from the received slaps. During the course of the streams, Mark encouraged the viewers to make donations for the sake of slapping Wade while loudly chanting the name of the Ham-Fisted Avenger.
Occasionally, Mark takes on an over-exaggerated persona based on the character of Shane Walsh from the popular drama series The Walking Dead (of which Mark is a big fan of). As Shane, Mark often makes crude remarks to Rick (Wade) about Lori (often played by Bob) and their relationship with her, as well as different comments about a variety of topics that somehow end up linking back to protecting Lori and Carl (also occasionally played by Bob). While speaking with Rick, he often blurts out a series of exaggerated variations of quotes from the show (e.g. "M-M-M'ask you sumthin'!" and variations of "You think you know me but you don't!") to try and prove a point.