The Mormaer of Caithness was a vassal title and a member of the Norwegian nobility since the Viking Age and until 1476.
The mormaerdom Caithness was intermittently held—presumably always as fief of Scotland— by the Norse Earls of Orkney, at least since the days of childhood of Thorfinn Sigurdsson in c. 1020, but possibly already several decades before. The modern reconstruction of holders of peerage earldoms do not usually include those of Caithness, although there is no essential difference between them and, for example, those of Mormaers of Lennox, Mormaers of Strathearn and Mormaers of Angus.
In 1334 the then Earl of Orkney, who was still a Norwegian vassal, was created or recognized as Earl of Caithness (see there for how the mormaerdom of Caithness continued as an earldom). In the true circumstances of 14th century this presumably was just a recognition of his hereditary right to the ancient earldom/mormaership of Caithness. Next year, all his Scottish titles were forfeited for treason. The next grant after Earl Malise's confiscation was to David Stewart, a younger son of King Robert II of Scotland.
The list is by necessity a fragmentary one, archives being not fully preserved, actual reign of some supposed mormaers being not fully attested, and so forth:
Donnchad of Caithness, (or Dungadr) whose wife was Groa, daughter of Thorstein Olafsson.
Thorfinn I of Orkney (Torfin mac Enar), possibly succeeding as Donnchad's son-in-law, husband of his daughter Gruaidh inghen Donnchaidh
Skuli Thorfinnsson of Orkney, son of Gruaidh and Thorfinn, mormaership (of Caithness) confirmed by Kenneth II of Alba
Lodvi Thorfinnsson of Orkney
Sigurd II Lodvisson of Orkney
1014– Thorfinn II of Orkney, mormaership of Caithness specifically given to him over his half-brothers by king Malcolm of Alba, his maternal grandfather
Madadhan of Caithness (apparently in Strathnaver, Muddan, Moddan), created mormaer of Caithness by king Duncan I of Alba in mid-1030s, killed 1040
Ottar of Thurso, son of another Madadhan, presumably a descendant of the previous Madadhan
Haakon I of Orkney, brother-in-law of Ottar and grandson of Thorfinn II
Arailt mac Haquin, Harold I of Orkney, nephew of Ottar, and son of Haakon; recognized in Caithness by king David I
Elga inghen Madadhan (Helga Moddansdottir)
Rögnvald Kali Kolsson of Orkney
Erlend III of Orkney, recognized of Caithness by Malcolm IV
Harold II of Orkney (Arailt mac Mataidh)
Harald the Young, grandson of Rögnvald Kali Kolsson, confirmed by king Uilleam I of Alba
Ragnald IV of the Isle of Man, given Caithness by king Uilleam I of Alba
David of Orkney
Iain mac Arailt mac Mataidh, John I of Orkney (murdered in Thurso 1231)
Magnus mac Gille-Brighde of Angus, earl of Orkney
Gilbert II of Orkney
Malcolm or Magnus III of Orkney
Magnus IV of Orkney
John II of Orkney
Magnus V of Orkney
?princess Catherine of Orkney
c. 1334–35 Maol Íosa V, Earl of Strathearn, earl of Orkney
Maud of Strathearn, and her husband Wayland de le Arde
Alexander de le Arde, in 1375 sold his hereditary rights to Robert II of Scotland
1375 – before 1389 David Stewart, Earl palatine of Strathearn
c. 1389–1390 Euphemia Stewart, countess palatine of Strathearn
1402–28 Walter Stewart, 1st Earl of Atholl
1428–31 Alan Stewart
1431–37 again: Walter Stewart, 1st Earl of Atholl (d. 1437) (forfeit 1437)
1452 George Crichton, 1st Earl of Caithness (d. 1455) (created 1452, resigned 1452)
1455–76 William Sinclair, Earl of Orkney, created 1st Earl of Caithness, great-grandson of Iseabail inghen Maoliosa, youngest daughter of Malyesu V of Strathearn and his designated heiress of Orkney
