Merlin served as the advisor of King Arthur for many years and was also the grand-wizard of Camelot who aided in protecting the city from all manner of mystical assaults, foremost amongst them being Morgana Le Fay and her evil son Mordred, who was blessed by his mother with magical-powers of his own.
Merlin was powerless to prevent the ultimate fall of Camelot when King Arthur sacrificed his life defeating Mordred in a great battle but he managed to end Morgana Le Fay's threat by casting her into the pits of Tartarus - he then proceeded to transport all of Camelot to a new dimension in order to preserve it for all of time as a place of magic and mystery.
Merlin would ascend beyond his former limitations during this time and became the guardian of all magic whose job was to safeguard the mystical world from evil and ensure that young sorcerers and would-be-gods were trained properly in the responsible use of their power - thus Merlin became, in essence, a cosmic entity and has remained so ever since.
Despite his great power Merlin still retains his humanity and compassion, refusing to utilise any of the dark-arts (black magic) and forbidding any under his care from doing so as well: only magic deemed as "white magic" is permitted by Merlin and as a result both he and his "champions of magic" rarely fight and are well-equipped to battle against the forces of darkness from their eternal castle in the "Rainbow Bridge".
Merlin is vastly powerful and a master of all magic, limited only by the fact he can only utilise "white magic" - this means he can't use hexes or spells that are powered by negative sources and must rely instead on elements, nature and other benevolent sources: this also leaves him vulnerable to attack from black magic.
- Omni-Magic (excluding black magic)