One of the most powerful magic users in fiction is Gandalf from 'The Lord of the Rings'. He is a wizard with great wisdom and the ability to use powerful magic like his signature spell, the white light that can drive away darkness and evil. Another is Dumbledore from the 'Harry Potter' series. He is highly skilled in various forms of magic, including powerful defensive and offensive spells, and has extensive knowledge of magic lore. Also, Doctor Strange in the Marvel Comics universe is extremely powerful. He can manipulate time, space, and dimensions with his magic, creating complex spells and shields.
In fiction, Merlin is often regarded as one of the most powerful magic users. In Arthurian legends, he has the power to see the future, transform shapes, and use magic to guide the destiny of King Arthur. Then there's Albus Dumbledore again. His magic is not only about spell - casting but also about his strategic use of magic in the wizarding world. He was able to hold his own against the most powerful dark wizards. And from the 'Chronicles of Narnia', Aslan has god - like magic. He can create and destroy worlds, and his magic is intertwined with the very fabric of Narnia.