Vance Petrol of Chugworth Academy is a thinly veiled Vin Diesel.
The titular character of King Of The Unknown is clearly Elvis, though he is never named as such. Ever since a supernatural mishap transformed him (into a fat slob) and forced him to fake his death, "the King" dedicated his new secret life to kicking supernatural ass for a The Men in Black-like Government Agency of Fiction known as the IRSU. Agent H, King's Mission Control at IRSU, is a similarly veiled and still-living Jimi Hendrix. Aside from the broad strokes, many small details are culled from the rock stars' lives to create these just-barely veiled versions.
Colonel Sassacre is clearly just Mark Twain wearing a wizard hat.
Rufioh's speech is patterned quite closely after that of Dante Basco's Tumblr account following Homestuck, and the character is both based on and named after a character Dante Basco played in Hook. Andrew Hussie's Author Avatar confesses the former in an Easter Egg on the flash where Rufioh is introduced.
Erfworld is a Parody World; this isn't just an artistic choice, it's an integral part of the world because people from the 'regular worlds' who, in fact, might be famous fictional characters from specific parallel universes where they are real can use their Genre Savvy and knowledge of pop culture to predict how units and leaders act and think based on how they look and the history of their 'regular world' counterparts. As such, a good quarter of the Erfworld is celebrity. Another quarter involves famous historical figures, and the rest come from various media.
Steve in Irregular Webcomic! seems to be Steve Irwin from Crocodile Hunter, but Word of God insists that these are not the same person. The annotation under #1288 says that the comic Steve 'might perhaps be somewhat loosely based on' Steve Irwin, 'if you believe the unrestrained hearsay and rampant speculation of some readers.' The rerun commentary for #7 provides a Suspiciously Specific Denial: 'Steve and Terry are of course not even slightly based on the real life Steve and Terri Irwin... The fact that "Terry" is spelt differently to "Terri" should absolutely and beyond a doubt confirm that in the minds of any lingering doubters, as it's clearly not a case of me making a mistake in a badly botched attempt to copy her name. '
Scary Go Round introduced Ben Bishop, founder of Zambian Computing. His and his company's history seems an awful lot like that of Steve Jobs and Apple. (His company — with rainbow logo — is revolutionary in the 80s; in the 90s he leaves the company for unspecified reasons, but returns to roll out an all-in-one computer; in the present day, his company — now with a pure-silver logo — has computers, tablets, phones, and "more money than any company on earth".)
Leif & Thorn features an author of a popular children's fantasy series, who bears more than a little resemblance to J. K. Rowling.
Curse Quest The Owl Hunter looks eerily similar to Steve Irwin the Crocodile Hunter, right down to the accent that's implied and his shorts. The Owl Hunter tracks down ulvorn instead of crocodiles and acts like a parody of the original.