Meringue the Malevolent is or was a human man.
Description
This evil sorcerer of unclear origin travelled to Mount Duckburg in the 10th century to collect mystical metals, which he fashioned into Orbs which he planned to combine into the Scepter of Power, using a ritual that could only be performed at the closing of a millenium. The druid Darfeld, with the help of local farmers Donaldo and Michael, managed to stall Meringue long enough to foil this plot, with the orbs ending up scattered into the far corners of the Earth, but, not to be so easily outdone, Meringue used another curse to seal himself, in unaging sleep, inside Mount Duckburg itself, knowing the Orbs would be reunited a thousand years later.
Meringue emerged from the Mountain as planned in 1999 and discovered the Orbs had indeed found their way back to Duckburg, in the hands of Michael and Donald's descendants: Mickey Mouse and Donald Duck. Though his understanding of the modern world was poor, Meringue's magic was still formidable enough that he very nearly succeeded, having mind-controlled several Calisotan badduns (the Beagle Boys, Magica De Spell and the Phantom Blot) into being his "private army".
However, the combined effort of Donald, Mickey and friends, plus the Blot betraying Meringue at the last moment, once again brought his schemes to a swift end. He'd come very close indeed to victory, having assembled the Scepter of Power, but the forces of good managed to render the Scepter unstable; the swirling magical energies created a wormhole that sucked in Meringue to parts unknown before vanishing altogether. Though it is possible he'd just been killed, Mickey Mouse feared he may still be out there in some form, possibly trapped in some alternate dimension.
Behind the scenes
Meringue the Malevolent only appeared in the various stories making up The Orb Saga, written by Pat & Carol McGreal, starting with War of the Wizards.
Due to their resemblance, a fan theory holds that Meringue is Yen Sid's brother, though that is mere unfounded speculation.