Mike Roessler, usually identified in adventures as Mr. Roessler, is a real-world middle school teacher cast by Eamon author Nathan Segerlind as an antagonist in many of his adventures. In his review of The Computer Club of Fear, EAG president Tom Zuchowski writes, "In case you are wondering, Mr. Roessler was Nathan's computer-education high school teacher. I understand that the poor gentleman was somewhat bemused by Nate's tendency to cast him as the villain in his Eamons!"
Segerlind depicts the fictionalized Mr. Roessler as a comically fiendish and tyrannical villain, often inhabiting a secret lair surrounded by henchmen, and almost always sporting plaid pants and wire-rim glasses. The real Michael Roessler is a retired educator who taught history and social studies at Portland Middle School in Portland, Michigan; he is also the author of Fourth Graders and Computers: A Case Study (1987).
In the introduction to The Pathetic Hideout of Mr. R., Segerlind notes that the name is "pronounced race-ler".
Roessler is the principal villain in two of Segerlind's adventures:
- The Computer Club of Fear. You're hired by a group of students to capture the "evil king" Roessler and safely return him to them. On his return, the students simply take him to a party to celebrate his accomplishment of earning his PhD in education.
- The Pathetic Hideout of Mr. R.. The immortal tyrant Roessler has established an outpost on Eamon and you're sent to destroy it. Though you can demolish the fortress and dispatch Roessler, he'll dissipate into black smoke laughing that he's invincible and will return.
He's also a recurring minor character in most of Segerlind's others works:
- Lost! — lurking in a secret chamber wielding a blade.
- The Lake — waiting on a small island.
- The Lair of Mr. Ed — in a classroom wielding a flame thrower.
- Ragnarok Revisited — as "Mr. Roesslersson", a Viking-esque fighter wearing plaid chain mail.
- Attack of the Kretons — aka "The Cheesedip God" in the town of Oigres.