Karl Thotep, previously known on the wiki as Purple, first appears in-comic next to Tarvek and Higgs as they stand on a balcony located in the depths of the undersea dome of The Queen's Society, preparing to intervene in the summoning by Snacky and his fellow Grey Hood conspiracy-members of another extradimensional being. Karl needs the duo's help, but has trouble explaining the specifics because he gets confused about whether he's talking about the past, present, or future. All of time is the same to him, which is how we know he's an extradimensional being.
After his arrival, his presence causes Tarvek and Higgs to start making short, random hops forward and backward in time between frames of the comic, Tarvek more than Higgs because, we soon learn, Higgs' extremely long life anchors him somewhat in time. Karl borrows some time-stability from Higgs to give to Tarvek. He also comments that Tarvek is scheduled to go mad at some point. This all deals a fatal blow to the whole "thwarting" plan, and the other Being finally snags Tarvek with a flailing tentacle, cutting the conversation short.
Karl next appears down on the main floor in media res, where he meets Dimitri Vapnoople, who tries to tell him why people need monsters, but can't quite explain himself because the Baron "took my words." (ie, drilled into various bits of his brain.) Karl can observe the confusion in Vapnoople's thoughts, is curious about what he would say if he could, and therefore, with a , repairs his brain. (Why Karl suddenly doesn't know what his conversation-mates are going to do or say is another unanswered question.)
This act turns out to be unfortunate, because, along with his words, Vapnoople regains his (typically crazy Spark) intention to improve the human race by creating monsters superior to people, so that only the best (smartest, strongest) human beings survive. Demonstrating his point, Vapnoople summons up a further mass of monsters to battle the one controlled by Snacky.
This distresses Karl, and he nervously lets Agatha and Tarvek use him as bait to lure all the critters in and reverse the summoning process. And then, when Vapnoople steps through the now-closing dimensional portal to go seeking after the power offered by the realm on the other side, and attempts to drag his unwilling new "apprentice" Agatha along with him, Karl pulls her and Krosp out of range. Once the portal is closed and the machine that created it reduced to slag, only Tarvek and Higgs can still easily see or hear Karl.
Back story Edit
Back home, Karl was "but a simple vozzler... Children love us!" For a clown(?) also to be a superb brain surgeon is particularly surprising - if we do not count that he is from a higher dimension, and his brain thus has the potential to be MUCH more complex than human one (all those additional spatial dimensions at least allow for the possibility of his neurons having an order of magnitude more connections).
It also turns out that he's been lurking about the dome before we and Our Heroes get to meet him; he was able to communicate with the now late Professor Homlomium, and his out-of-dimensional-phase presence evidently provoked stories of "The Boilerghast" among the other dome inhabitants.