Cornelius Sigan

"He could change day into night, turn the tides, and legend has it, his spells helped build Camelot itself."

- Gaius on Sigan

Cornelius Sigan was the greatest sorcerer Camelot has ever known, before Merlin.

Early Life
It is said that when he was first alive he could turn the tides, change day into night, and even helped build Camelot itself. His life's mission was to defeat death and he swore to one day return from the grave. Sigan became too powerful and the King at the time ordered him to be executed. Before his death, Sigan cursed Camelot, saying that he would one day return and raze the city to the ground. It was said that he didn't want his wealth and power to die with him and that up until his execution he worked on a way to cheat death.

Return
This is revealed to be true hundreds of years later. After Camelot miners uncover his tomb, a thief called Cedric works his way up to a position in the Royal Household and uses this to enter the tomb. He intends to steal Sigan's riches and jewels, including a large blue heartshaped jewel that one of the miners, Tom, drunkenly told him about. The jewel contains Sigan's soul and when Cedric breaks the jewel out of its setting, he becomes possessed by Cornelius Sigan's soul. Sigan subsequently launches an attack on Camelot that forces Merlin to ask Kilgharrah for help.

After witnessing Merlin's magic, Sigan suggests that he and Merlin form an alliance. However, when Merlin rejects the offer, Sigan leaves Cedric's body and attempts to possess him in order to bind their powers. Using a spell that Kilgharrah recently taught him, Merlin is able to trap Sigan's soul back inside the jewel. Uther has the vault where the tomb and soul of Cornelius Sigan lay resealed (The Curse of Cornelius Sigan).

Post-mortem
Gaius would ultimately acknowledge Merlin as "the most powerful sorcerer who has ever lived." (The Secret Sharer)

Abilities
Cornelius Sigan was described as one of the most powerful sorcerers ever to live. Although he is only shown once in the series, he is shown to be an extraordinarily powerful individual. While he was alive, he was said to be able control the tides and change night to day. His powers were so great that he was able to immortalise his own soul, keeping it alive after his death by containing it in a jewel.

Upon gaining a new body, his powers remained intact, as he was able to possess another and could animate and control every gargoyle in Camelot. He was only defeated by an ancient and powerful spell that the Great Dragon told Merlin, which trapped his soul back inside the jewel.

Trivia

 * According to Gaius, " In the Old Religion, the name Sigan means raven."
 * Cornelius Sigan shares similarities with the character of Lord Voldemort from the Harry Potterseries by J.K. Rowling, which are:
 * Both are sorcerers with immense powers.
 * Both seal their soul, either partially or wholly to an object as means of gained immortality.
 * Both have a strong connection to an animal; Voldemort's nostrils were slit like a snake's, he had a pet snake, and he belonged to the Slytherin house and was the heir of Slytherin himself, both of which are symbolised with a snake. Sigan's name, in-universe, means 'raven', and he wears black feathers that likely belong to the same animal, or are at least meant to represent ravens.