This is a famous 'Border Country' surname, and claimed by Scotland although with some English origins. The surname derives from the lands of Blackadder on the banks of the river Adder, in the county of Berwickshire. The origination lies in the Olde English words 'blaec' meaning 'black', but possibly in this context 'deep', plus 'adar'- 'winding' - a deep, winding, river. The surname is first recorded in the 15th century as shown below, and was apparently popular in Lanarkshire at one time. Before the end of the 15th century it had achieved considerable trust and hence status, with Adam de Blacathair being sent by the Scottish Parliament to guarantee safe conduct to the envoys of Princess Cecillia's dowry on its way to Edinburgh in 1477. In 1486 another member of the clan, Charles Blackater (so much for medieval spelling), was granted a safe conduct to pass into England, suggesting that the clan held some Scottish diplomatic position in the period after the end of the English 'War of the Roses'. Perhaps the earliest member of the clan to achieve international fame was Robert Blackader (also known as Blacader), Archbishop of Scotland, who died on pilgrimage to the Holy Land in 1508. John Blackadder, known as John the Elder, 1615 - 1686 was a famous divine, who never seemed to be on the right side. He was finally arrested and imprisoned on Bass Rock, where he died! His son, John the Younger, took to the military life, ultimately being appointed Governor of Stirling, where he died in 1729. The first recorded spelling of the family name is shown to be that of Blackadir de Eodem, which was dated 1426, in the annals of the earldom of March, during the reign of KIng James 1 of Scotland, 1406 - 1437. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.