A natural stone with a hole in the center and gift from the earth to the lucky finder.
A totally throw away .. cannon fodder ..shove it in the mouth of the monster and run for it type of character. Useful though for ‘taken with a pound of salt’ information and running small unsavory errands.
A rumour of the knights of some powerful king that sleep until danger threatens the kingdom.
The truth is that they were rebels, trying to split the kingdom. Once captured they were put into an enchanted sleep, protected from age and harm, until their aims have been carried out by others in which case they will awaken.
There is a loophole in the spell in that trying to take one of their weapons will also awaken them.