Grainne was the name of a Celtic sun-goddess, as well as the 16th-century Irish pirate queen, Grainne O'Malley (also called Granny Malley and Grace O'Malley), a contemporary of Elizabeth I of England.
Oh, and let's not forget the valiant Gráinne Mhaol (or Gráinne ní Mhaille, or her Anglicized name, Grace O'Malley), famed pirate queen of Connacht, who lived at the time of Elizabeth I.
A musical has been made about the adventures of Grainne (Grace) O'Malley. It's called The Pirate Queen and premiered in Chicago in 2006. It is now on Broadway if you want to see it!