Yen Sid

Yen Sid is a powerful sorcerer who made his first appearance in Disney's 1940 animated feature, Fantasia. He appears in Kingdom Hearts Birth by Sleep, Kingdom Hearts II, Kingdom Hearts coded, Kingdom Hearts 3D: Dream Drop Distance, and Kingdom Hearts III as a retired Keyblade Master who is renowned for his wisdom and magical prowess. Yen Sid keeps a close watch on the balance between light and darkness; he was once King Mickey's master and taught him everything he knows about magic and the Keyblade.

Kingdom Hearts Birth by Sleep
The Sorcerer's Apprentice (1940)

''A great sorcerer who dwells within the Mysterious Tower. Mickey is his apprentice.''

Yen Sid was the first to detect something amiss with the worlds, and alerted Master Eraqus as soon as he could.

''He is concerned about his apprentice, Mickey, who has run off. ''

'' It was also he who delivered to Aqua the news of Master Eraqus's demise at the hands of Terra and Master Xehanort. ''

Kingdom Hearts II
The Sorcerer's Apprentice (1940)

''A powerful sorcerer, second to none. He tutored the King in magic.''

''From conjuring up skies full of beautiful butterflies to parting an ocean, Yen Sid's feats of wizardry are...well, amazing. His name alone fills some folks with awe.''

''Yen Sid shared some of his wisdom with Sora and his friends. He also taught them some valuable techniques to help prepare them for what they'll face on this new quest.''

Kingdom Hearts 3D: Dream Drop Distance
"The Sorcerer's Apprentice" (1940)

''A great sorcerer who watches over the balance between light and darkness. He was also King Mickey's teacher.''

With a new threat looming ever closer, he has decided Sora and Riku must be examined for the Mark of Mastery.

Trivia

 * Yen Sid's name is an anagram of "Disney," a tribute to Walt Disney himself.