It may be slighty vague, God of Evil100. Actually, what i mean is do you know any villains that share similarities with King Stefan in these terms:
1. Both are male.
2. Once befriend with a misunderstood protagonist in the past, but then betray them and cause the said protagonist became bitter and they became enemies.
3. Both initially shows no sign to become a villain, but at time passes, they became quite villainous.
4. Both highly sadistic, and also held a deep hatred for the protagonist that they betrayed after betray them.
If you ask me, I have one albeit quite vague: Anime version of Halloween from MAR franchise. I mean:
1. Halloween was initially not show any sign to become a villain/threat like King Stefan does.
2. Both Halloween and King Stefan once befriend with with a misunderstanding protagonist (Alan for Halloween and Maleficent for King Stefan) though in Halloween case, Alan was not as misunderstand as Maleficent did as Alan simply lonely.
3. Halloween later betray Alan like King Stefan did, though the circumstance of the betrayal was not same (King Stefan betray maleficent by steal her wings while Halloween, on the other hand, betray Alan by not seeing error of his destruction, murder those who once bullies him, steal his fire ARM, and mocks him as a hypocrite before left). Although not same, both case left the betrayed protagonist traumatized, albeit Maleficent's pain was far bitter than Alan had, as maleficent ended up to the dark side for a brief moment.
4. Finally, both King Stefan and Halloween grown as sadistic individual, enjoys tormented protagonist that they betrayed in the past at the final battle.