The Fleming surname derives from the words "le Fleming" that were used by scribes in Norman England as an epithet (or by-name) to distinguish individuals from others with the same name.
An epithet is an adjective or phrase expressing a quality or attribute regarded as characteristic of the person or thing mentioned. For example, before he conquered England in 1066 the epithet of William (Duke of Normandy) was le batard (the bastard) because his parents never married. After his success at the Battle of Hastings his epithet was changed to le conqueror (the conqueror).
The Norman court included some individuals whose epithet was le Fleming (French). It was often written as Flamang in Scottish charters or in Latin as Flandrensis or Flamaticus. All of these epithets indicate that the person had Flemish origins. In many cases this epithet was also applied to their descendants and some (but by no means all) of these eventually adopted it as their surname.
William's army at the Battle of Hastings in 1066 included not only Normans but contingents from Brittany, Maine, north-eastern France and Flanders as well as smaller numbers from other parts of Europe. After his victory, many of these were rewarded with English estates. Twenty years later these were recorded in the Domesday Book, including several Flemish magnates such as Baldwin, Erchenbald, Frederic, Hugh, Humphrey, Odo, Ranulf, Roger, Walter and Winemar.
Forty years later King David I ascended the Scottish throne accompanied by his wife Maud, of Flemish stock. She brought with her numerous Flemish protectors. It is noteworthy that, while they all had Flemish ancestry, many of them had actually been born in England since 1066.
The descendants of most of these "Flemish" newcomers later adopted surnames other than Fleming. The Flemish origins of many significant Scottish families are well documented, including those of Baird, Baillol, Beaton, Biggar, Brodie, Bruce, Cameron, Campbell, Comyn, Crawford, Douglas, Erskine, Graham, Hamilton, Hay, Innes, Lindsay, Murray, Oliphant, Seton, Stewart and Sutherland.
Thirty years after the ascension of David I, the English King Henry II expelled numerous men of Flemish heritage from England, so it made sense for some of those to join their compatriots in Scotland. Many Flemish incomers and their descendants who settled as knightly tenants of David's son Malcolm IV (r. 1153-65) left their mark on the place names of Upper Clydesdale in particular: Simon Loccard (Symington), Wice or Wizo (Wiston), Tancred (Thankerton), Lambin (Lambington), and Robert, brother of Lambin (Roberton).
The descendants of at least one of these "Flemish" immigrants to Scotland later adopted Fleming as their surname. This must have happened during the 13th century because Robert Fleming (founder of Clan Fleming) who was born in about 1280 was always known by that surname.
Details of his origins are obscure. He clearly did not descend from Baldwin of Biggar because the Biggar estate devolved eventually on an heiress, Marjory of Biggar. This land came into the Fleming family by marriage. He probably had at least one elder brother who inherited their father's primary estate although Robert's heir Malcolm seems to have inherited an estate at Fulwood in Renfrewshire from him.
There were many men with the epithet Flandrensis, Flamang or le Fleming in Scotland in the early to mid 13th century. Since Robert Fleming was born three or four decades later, he could be the son, grandson or great-grandson of any of them. Historians have not, so far, definitively identified Robert's ancestors.