History does strange things to names, this is an example. The present spelling is an anglicized dialectual variant (hence its rarity) of the Celtic Duncan or Duncum, which first appears as 'Donnocatus' from the pre 10th century and does translate as 'the brown warrior', or possibly 'fort warrior'. The name is first recorded as a Scottish surname in the 14th century, the alternative spellings since then have been Dunckane (1424) Dokan (1516) Doukane (1527) - all Scottish whilst the English records include Dunkon (1379) and Duncum (1497) etc. The first recorded spelling of the family name is shown to be that of John Dunkan. which was dated 1367 Land Charter of Berwich. during the reign of King David 11 of Scotland 1329 - 1371. 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.