Evidently a Hobbitish word created by chopping the 'chief' off the word 'chieftain', the Hobbits first chose a Thain to rule them when Arvedui, last King of Arnor died.

Over time the Thain became a hereditary position, originally held by the Oldbuck Clan. Since 1740 SR, the Thainship has remained within the powerful Took clan.

In the Fourth Age the title in Sindarin was Ernil i Pheriannath ("Prince of the Halflings"), after Peregrin Took became the Thain.

Other rulers of the Shire include the Master of Buckland and the mayor of Michel Delving in the White Downs, as well as in the Fourth Age the Warden of Westmarch, a position created by King Elessar