I suppose the term's a bit of a misnomer – the only real quantifiable feature is that they've made enough of a mark in history, legend, or something else that they're able to potentially be summoned from the Throne. They don't necessarily have to be heroes, and certainly don't have to be just to be considered.

[ coughs. anyway, ]

I do. I can make anything I can hold into a copy of the holy sword Excalibur – even things not normally feasible in a fight.

[ The other one's kind of hard to explain, since they're not around right now, anyway, so... he's just gonna ignore that one. ]