Perhaps Neville Longbottom could take on this role. He has shown great courage throughout the series. His experiences with loss, like the death of his parents, could lead him down a path where he becomes the apprentice of death, using his newfound powers to protect others and bring a new balance to the wizarding world.
Well, obviously Harry Potter himself is a common character. And his mentor, who could be an original character created by the fanfiction author or an existing character from the wizarding world like Albus Dumbledore in a different role as a more hands - on master.
In 'harry is an apprentice fanfiction', apart from Harry, there might be other apprentices too. They could be his friends or rivals during his apprenticeship. Also, we can't rule out the appearance of some of the main antagonists from the original series, as they might try to interfere with Harry's apprenticeship journey.
The apprentice's character development can be shown through their changing views on magic. At first, they might be in awe of Grindelwald's powerful and often dark magic. But as they learn more, they start to see the harm it can cause. For example, if they witness Grindelwald using a spell to harm innocent people, it could make them question their loyalty.
There are often fanfictions where Harry is apprenticed to a character who has a different magical specialty. For example, he could be apprenticed to a potions master who teaches him ancient and forgotten brewing techniques that help him in future battles or adventures.
One common theme is the exploration of hidden magical knowledge. Since Harry is Dumbledore's apprentice, he gets access to things that other students don't. Another theme is the deepening of their relationship, showing a more father - son like bond between them.
One interesting aspect could be how the author reimagines Harry's character in the context of being an apprentice. Maybe he has a new set of skills to learn or different relationships to form compared to the original story.
Obviously, Harry Potter himself. And there could be Dumbledore, who might guide Harry in this new path related to Merlin. Also, Hermione and Ron could be there, either helping Harry or being a bit skeptical about this new adventure.
Well, it could be about Harry Potter discovering some long - lost magic that was once taught by Merlin. Maybe he stumbles upon an ancient spellbook or a hidden place where Merlin's teachings are preserved.
I'm not sure about a single definitive 'Harry is Dumboldores Apprentice' fanfiction. But in general, such fanfictions usually explore the relationship between Harry and Dumbledore in a more in - depth way compared to the original books. They might show how Dumbledore imparts his wisdom and knowledge to Harry, which can be really fascinating to read.