William Sinclair, 1st Earl of Caithness
He was the grandson of Henry Sinclair, 1st Earl of Orkney and son of Henry Sinclair, 2nd Earl of Orkney, for a time protector of the young James Stewart, the later James I of Scotland. He was Lord High Admiral of Scotland, and was Lord Chancellor of Scotland from 1454 to 1456. He became the first Lord St. Clair in Scotland in 1449.
He made several big territorial transactions during his life.
The first important one was the exchange of his inherited lordship of Nithsdale to the estates of the earldom of Caithness - which soon led to his obtaining the title of Earl in the peerage of Scotland.
King James III gained his hold and rights of the Norwegian Earldom of Orkney for the Scottish Crown in 1470 (see History of Orkney), against a promised compensation (it turned out to be lands of Ravencraig, in 1471); and William Sinclair was thereafter Earl of Caithness alone until he resigned the Earldom in favour of his son William in 1476.
In 1471 James bestowed the castle and lands of Ravenscraig in Fife on William Sinclair, in exchange for all his rights to the earldom of Orkney, which, by an Act of the Parliament of Scotland, passed on 20 February 1472, was annexed to the Scottish crown.
He was married three times, first to Lady Elizabeth Douglas, daughter of Archibald Douglas, 4th Earl of Douglas; secondly to Marjory Sutherland, daughter of Alexander Sutherland of Dunbeath, and lastly to Janet Yeman.
By Lady Elizabeth Douglas (ca. 1408-1451):
- William Sinclair, 2nd Lord St. Clair (1436) was, in the opinion of the father, a wastrel, wherefore he was disinherited. His family received only the Castle of Ravenscraig in Fife.
- Catherine Sinclair, married Alexander Stewart, Duke of Albany
- (second daughter, name not recorded)
By Marjory Sutherland (married 1456):
- Sir Oliver Sinclair 1452
- William Sinclair, 2nd Earl of Caithness. 1460-1513
- Alexander Sinclair ca.1454
- George Sinclair ca.1453
- Robert Sinclair 1447
- Arthur Sinclair ca.1452
- Eleanor Sinclair, 1457-1518 married John Stewart, 1st Earl of Atholl
- Elizabeth Sinclair, c.1455-1498, married the Laird of Houston
- Margaret Sinclair, ca.1450 married David Boswell of Balmuto
- Katherine Sinclair 1440-1479
- Susan Sinclair ca.1451
- Marjory Sinclair 1455-80
- Mariota Sinclair ca.1455
The earl's second son of his second marriage, William Sinclair, 2nd Earl of Caithness, became the designated heir of the Earldom of Caithness and continued that title. The Barony of Roslin went to his first son by that marriage, Sir Oliver Sinclair.
All in all, the Sinclair ancestry is well and thoroughly represented in Scottish and British high nobility, thanks to marriages of his daughters and other descendants. William's daughter of his second marriage, Lady Eleanor Sinclair, married John Stewart, 1st Earl of Atholl, a relative of the kings. Lord Henry Darnley and his son James VI of Scotland descend from Eleanor, and through them, many royal houses of Europe. His other daughter by this marriage, Katherine Sinclair, married Alexander Stewart, 1st Duke of Albany, a nephew of the said Atholl.
- Ravenscraig Castle
- Balfour Paul,vol ii, pp333-336
- Charles Mosley, Burke's Peerage and Baronetage, 107th edition.
- Sir James Balfour Paul, The Scots peerage : founded on Wood's ed. of Sir Robert Douglas's Peerage of Scotland; containing an historical and genealogical account of the nobility of that kingdom. Edinburgh 1904. 
|Peerage of Scotland|
|Earl of Orkney
|Earl of Caithness
George Crichton, 1st Earl of Caithness
|Lord High Admiral of Scotland||Succeeded by
David Lindsay, 5th Earl of Crawford
William Crichton, 1st Lord Crichton
|Lord Chancellor of Scotland
Andrew Stewart, 1st Lord Avandale