In early medieval Scotland, a mormaer was the Gaelic name for a regional or provincial ruler, theoretically second only to the King of Scots, and the senior of a Taoiseach (chieftain). Mormaers were equivalent to English earls or Continental counts, and the term is often translated into English as 'earl'.
The etymology is variously debated as "Great Steward" (incorporating Gaelic and Picto-Latin), or "Sea Lord" (perhaps defenders against Vikings). Historians do not know whether the institution was Gaelic or Pictish. However, since mormaer occurs only in the post-Pictish period, it is difficult to argue for Pictish origins. There is also debate whether mormaer was simply the east-coast equivalent of kinglet (Gaelic: ruirí or rí). For the earliest periods, there is uncertainty about the difference between a mormaer and a Taoiseach (Modern Scottish Gaelic tòiseach 'chief'). The earliest Scottish Latin sources use thanus (thane) for toisech; this word was adopted from the Anglo-Saxon lands to the south. It is possible that thanus, comes, mormaer and toisech all originally meant similar things, or at least were not elements of a stratified hierarchy.
The office of mormaer is first mentioned in the context of the Battle of Corbridge (918), in the Annals of Ulster. The first individual named mormaer was Dubacan of Angus, one of the companions of Amlaib, the son of King Causantín II (Constantine II). His death at the Battle of Brunanburh (937) is recorded in the Chronicle of the Kings of Alba. He is mentioned as Mormaer of Angus (Gaelic:"Mormair Oengusa', or 'Mormaer Óengus).