Hans from Frozen was turned evil by the rock trolls.

In the song Fixer Upper, they say ‘Get the fiance out of the way and the whole thing will be fixed.’ Shortly after, we see Hans be evil for the first time in the film.

In addition, at the beginning of the film, the grand troll notes that it’s lucky the magic hit her head and not her heart, because the head can be persuaded. So we have motivation, capability, and a stated intent.