William Sinclair, 1st Earl of Caithness, last Earl of Orkney, Baron of Roslin, was a Norwegian and Scottish nobleman and the builder of Rosslyn Chapel, in Midlothian.
Spouse: Lady Elizabeth Douglas
Sir William Sinclair, (1410 - 1484) son of Lady Egidia Jill Douglas
Knight Templar, Builder of Rosslyn Chapel
Sir William was a Norwegian and Scottish nobleman. He was confirmed as Jarl of Orkney by King Eric of Norway. He was a possible heir to the Norwegian crown after the death of King Christopher in 1448. For a time he was the protector of the boy King James I of Scotland. He was Lord High Admiral and Chancellor of Scotland.
In 1468 William accepted the castle and lands of Ravenscraig in Fife from King James III in return for any rights on the Orkneys and Shetlands. He surrendered Nithsdale for Caithness and he held lands in Sutherland. The family links to Douglas, Sutherland and Stewart remained strong.
He laid the foundation stone of the Collegiate Church of St Matthew, Rosslyn Chapel 1446.
The earl's second son of his second marriage to Marjory Sutherland, William Sinclair, 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 the 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 of Scotland. Lord Henry Darnley and his son, King James VI of Scotland, descended 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 1st Earl of Atholl.