A Donatário, a Portuguese word roughly meaning 'endowed' sometimes anglicized as Donatary, was a private person (often a nobleman) who was bestowed by the Crown with a considerable piece of land, called a donátaria, which was handed over at his discretion, exempt from normal colonial administration through some royal governor etc., so de facto equivalent to a British Lord Proprietor.
The system was applied to several colonial (later?) captaincies in Brazil.