I've kinda already looked at this~
Check the bottom of this page :
http://www.cavestory.org/forums/threads/152/
and then...
http://www.cavestory.org/forums/threads/152/
the first few posts on this page...
And finally to prove he is human ~!
The last Demon Crown owner is refered to as human :
*SUPeR SPoiler!* [look for the astricks!]
Back then, a huge number of robots were sent to this island
from countries on the Earth's surface.
Their target was the awesome power kept within this island...
The Demon Crown.
But you and I, we were different.
The two of us were sent in order to destroy that power.
When we got here, the island was in shambles.
The robots had torn it all to pieces...
And countless Mimigas had been slaughtered...
It was... terrible...
*****Finally, one man got the Demon Crown in his possession.
The robots' work was done, and the island fell silent.
But that was just the beginning of the tragedy.
******With the crown in hand, the man turned the Mimigas into killers
*and began his assault on the Earth.
*I tried to stop him.
*You were there too.
I wish my mod was already created and out there
EDIT: and if you want to be literal to what Pixel shows, in the intro where the Doctor approaches the Demon Crown... All that's left of the previous owner is his head