I'm looking for a translation of "Crâne de piaf", in English, in the context of a nickname given to some fictional character.
Also, take note that I am native from France. What I'm looking for, precisely, is an english nickname equivalent of "crâne de piaf".
A little more context is probably welcome: the character I'm thinking about was a very highly intelligent guy, an inventor, a physician, etc. But, at some point he progressively lose his humanity, by becoming something close to an undead. His intelligence is progressively reduced to that of a typical undead in fantasy books/stories.
One day, as he progressively becomes undead, his skull becoming more apparent (but not completely), he visits a little girl he used to know before the beginning of his transformation. And she do not recognize her. Instead, she calls him "crâne de piaf".
Much later, he will become a threat for all living being in the region and take this name - because he do not recall his real name.
What would be a good english equivalent for this name ?