Some say these are the same person, others not. Personally, I see them as separate characters.
Ban of Benwick
Bane, Bans, Bando, Bano, Liban, Pant
The King of Benwick (Benoic, Benoye, etc.), brother of King Bors, and father of Lancelot of the Lake and Hector. [More]
Ban of Gomeret
The King of Gomeret (Gormeret). [More]
When Gwenbaus decided to stay behind in Britain with his princess in the Forest Perilous (or Forest Perdue), his brother King Ban of Benwick left his crown with them. Gwenbaus enchanted the forest grove.
The crown may not have been magical in itself, but it gained a magical association; the enchantment was not broken until Lancelot came, sat in the chair, and wore the crown.