Clarke will run the half-marathon while wearing superhero garb as a way to raise money for Toronto's Hospital for Sick Children.
He's also out to break a Guinness world record for running the fastest half-marathon while dressed as a superhero.
Clarke isn't running in tights because he wants to fight crime or has an unhealthy appreciation for superheroes.
Clarke, who is now 36, spent three months undergoing treatment at Sick Kids as a child. He wants to run and raise money as a way to show his appreciation for the staff who once treated him and support the patients who are there now.
"It was such a hard time for my family," Clarke told CBC News. "To try and boost my spirits, they always called me their little superman. I want to pay it forward to all the kids who are still at Sick Kids. To show that sick kids are all around us."
When he was six, Clarke was treated at Sick Kids after coming home with a sore leg that got progressively more painful. His doctors struggled to diagnose his condition. At one point they feared leukemia, but eventually the symptoms seemed to disappear, he said.
"I seemed to go into remission — whatever it was, it went away," Clarke said.
Clarke, an elementary teacher at Ionview public school, has turned a few heads in recent months as he takes his training runs (while wearing the Superman suit of course) along the waterfront.
Abiyan Muse will be cheering for Clarke. Abiyan spent months at Sick Kids after undergoing open-heart surgery.
"I couldn't walk that much," Muse told CBC News. "Now I can walk, go upstairs and eat food very well."
He too plans to follow in his teacher's footsteps by running his own marathon one day as his favourite superhero: Batman.
Or, as he puts it: "The one and only Batman."
The Scotiabank Toronto Waterfront Marathon takes places Oct. 19.