One could argue that Merlin from Arthurian legends is the most powerful sorcerer in fiction. He has the ability to see the future, transform shapes, and use powerful magic to aid King Arthur. His magic is often portrayed as being very ancient and mysterious.
Dumbledore from the Harry Potter series is also a strong contender. He is highly skilled in a wide range of magic, including powerful defensive and offensive spells. He also has great wisdom and knowledge of magic which allows him to outwit many powerful dark wizards. He can perform feats like creating powerful protective enchantments around Hogwarts.
Gandalf from The Lord of the Rings is extremely powerful. He is a Maiar, a being of great power in Middle - earth. He can use his magic to fight against the forces of Sauron, such as using his staff to send out blasts of energy. He also has the power to inspire and lead others, which is an important aspect of his power.