The protagonist is the primary character in a story. While a story can have multiple main characters, the protagonist is the focus of the story.
James Zanasiu is considered the main character of the Darwin's Soldiers role-plays, while his Furtopia counterpart is the protagonist of Darwin's Soldiers (Furtopia). Dr. Jan Orlich is the main character of the reboot and James Zanasiu Jr is the main character of Chasing Seconds. The traveller is the protagonist (and only character) of Find the Cure!