What are Boos ghosts of?

[YoshiWrangler]

I've wondered this for quite a while, if Boos are ghosts, what were they in life? After some consideration I've come up with a disturbing answer.
Kirbys. Boos are dead Kirbys.
The physical resemblance is startling. Big circles with stubby, fingerless arms. Same eyes. They even blush the same. Of course Boos don't have feet, but then neither do traditional depictions of human based ghosts. Boos also don't inhale their enemies, but then the dead don't breath...
As for why dead Kirbys (members of Kiry's species, also known as "Puffs" by some Kirby fans) would antaganize Mario, who can say? Perhaps their current condition is punishment for a life time of randomly eating anyone unlucky enough to cross their path. Just keep in mind, the next time you run out of lives in Dreamland, you've not only lost a game.
You've made a Boo.

[Serum]

...that's a very good question. I always assumed Boos were born ghosts-- like, they're a race of ghosts, born and bred to be ghosts.

[Redstar]

I like your theory, but it simply makes more sense that Boos are an existing "race" of interdimensional energy. I don't see any reason to assume they are explicit ghosts of once-living creatures.

[Serum]

Just gonna leave this here...

[LBD_Nytetrayn]

This is my favorite theory.