- Fans generally assume that Gwen's mother is dead (often she is said to have died in childbirth, to parallel Ygraine) and that Merlin was named for the falcon.
- They also sometimes use 'Ambrosius' and 'Myrddin Wyllt' as some of the 'many names' for Merlin mentioned by the Dragon.
- Whether Gaius being Merlin's uncle is this or, Word of Actor (Richard Wilson believes Hunith to be Gaius' sister) or Word of God is a matter of some confusion.
- Also, some fans say that Merlin is a warlock and not a sorcerer because he was born with his powers, and sorcerers have to learn magic. This is because Merlin is referred to as a warlock in the show, but all others are called sorcerers (some fanfiction has him angrily defending himself against accusations of being a sorcerer on these bounds). However, it's never addressed in the show, so we don't know if that's canon or not.
- The existence of 'real' Arthurian legend also provides a huge source for fanfics, such as Mordred being Morgause's son.
- It's often speculated that Morgana's father Gorlois was killed due to a Uriah Gambit organized by Uther. Thing is, the circumstances of Gorlois's death were described in season 1 (that he was sent into battle and Uther neglected to send him reinforcements). At the time, there was no reason to suspect Uther deliberately withheld them. By the time season 3 rolled around, the writers had decided to make Morgana Uther's biological daughter (after he had an affair with Gorlois's wife). The Retcon of Morgana's parentage throws a very different light on Gorlois's death, though it's never speculated on in the show itself.
- There's a common idea that Sir Leon knows about Merlin's magic (and may even be a magic user himself), given the fact that he's known Merlin for almost as long as Arthur has, and may not be blinded by the same prejudices. The latter idea, of him being a secret magic-user, mostly stems from how often he gets thrown into walls/knocked unconscious/attacked by the Monster of the Week, and yet still manages to survive unscathed.
- Fans frequently toy with the idea that all the Arthur's knights actually know Merlin had magic the entire time and are keeping it a secret. They all know exactly how loyal Merlin is to Arthur and Camelot and they've seen for themselves how much Arthur depends on him for moral support. It doesn't hurt that he's just a genuinely nice guy, either. So, they all keep quiet so their friend doesn't get exiled or executed on the grounds of having magic.
Fanon / Merlin (2008)