Well, Harry is the central figure through which the story unfolds. The four founders play crucial roles as they are the ones who created Hogwarts. In addition, we might also see some of Harry's friends in the original series like Hermione and Ron, but they might be in a secondary role compared to Harry's interactions with the founders.
The main characters are Harry and the four founders. But there could also be antagonists. In some fanfictions, a dark wizard from the founders' era who was once defeated but is now trying to rise again could be an antagonist. Harry, with the help of the founders' wisdom and magic, has to stop this dark force from destroying Hogwarts and the wizarding world.
You'll usually find characters like Godric Gryffindor, Salazar Slytherin, Rowena Ravenclaw, and Helga Hufflepuff. They might be present in spirit or through memories stored in the staff. And then there are the modern - day students who stumble upon the secrets of the staff. They could be original characters created by the fanfiction writer or minor characters from the original books who are given more depth in these stories.
Well, obviously Harry would be the main character. Since he's the heir of the founders in this fanfiction.
Obviously, Harry is one of the main characters. There might also be his friends like Ron and Hermione. Since it's about being a founders heir, perhaps there will be appearances from the ghosts of the founders or characters who are descendants of the founders' friends or foes.
Typically, the main characters are the founders of the important ninja clans in Naruto. So, Hashirama Senju, who was known for his great strength and ability to control wood. Tobirama, his brother, was also a very powerful ninja. Madara Uchiha, the fearsome Uchiha leader. And Izuna Uchiha, Madara's younger brother. In the fanfiction, we might also see other characters who were associated with them, like their friends, comrades, or early adversaries, but the founders are the main focus.
The four founders themselves are usually very popular. Godric Gryffindor is often a favorite, as his trait of bravery is something many readers admire. His adventures and decisions in the fanfiction can be really exciting to follow.
Often, the main characters would be the heirs themselves. There could be a character who is the heir of Gryffindor, perhaps a young student who has always shown great courage and a sense of justice. Another main character might be the heir of Slytherin, who at first seems a bit of an outcast because of the negative reputation of Slytherin but turns out to have a complex and important role.
Obviously, the four founders - Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw and Salazar Slytherin are main characters as they are being reborn. They bring their unique personalities and magical abilities back to the story.
The apprentice is obviously one of the main characters. They are likely to be a young wizard or witch with great potential. Then there might be characters representing the different houses of Hogwarts, like a descendant of Gryffindor who is a mentor to the apprentice. There could also be a rival apprentice who has different ideas about the founders' magic.
The Death Eaters could still be antagonists. Even if Harry is the heir of the four founders, Voldemort and his followers would not want him to gain more power. They would try to undermine Harry's new - found status and use it to their advantage, perhaps by spreading false rumors about him among the wizarding community.
In the context of the Harry Potter universe, the founders are Godric Gryffindor, Salazar Slytherin, Rowena Ravenclaw and Helga Hufflepuff. In this fanfiction, it's likely these are the founders who are training Harry.