Being a Star Wars fan and looking to get more attention to help his fund-raising efforts, he first wore the outfit for the marathon three years ago.
He has raised more than £20,000 for Make-A-Wish and Spread a Smile, but now he feels it’s time to hang up his helmet.
“I don’t want my family and friends to get bored of me as the running stormtrooper,” he said, adding that it felt right to round it off as a “trilogy” in Star Wars’ fashion.
Seeing Sunday as his “lap of honour”, he’s not even going to try to break the Guinness record he set last year – the fastest Star Wars character at 4:59:12 – due in part to the heat.
“I’m going to stop and talk to as many people as I want along the way,” he said.
After all, he says, it is the crowd’s smiles that make the day for him, especially when he sees children’s reactions to his costume and knowing “you’ve made their day”.