King Estmere (perhaps meaning King of the East Moor/mere/muir): Fictional character from the poem of the same name, found only in the famous Percy folio manuscript. Bishop Percy however tore out the pages, which have been lost, so we have only the copy of the ballad as Percy rewrote it.
As best we can tell, King Estmere courts the daughter of King Adland and wins her love. But she is to be wed to the King of Spain. Estmere attends the wedding disguided as a harper, kills the Spanish king, and wins the girl for himself.