Some years ago historian Gordon Lucy wrote a book entitled The Ulster Covenant: A Pictorial History of the 1912 Home Rule Crisis. In it he said:
The Presbyterians, with their tradition of sturdy independence, the very backbone of Ulster Unionism, were well acquainted with the concept of the solemn covenant in the religious history of Scotland in the sixteenth and seventeenth centuries. The concept came from that tradition but the content of the Ulster Covenant owed much to more recent events.The Covenant text was the inspired creation of one man. Thomas Sinclair, a wealthy Belfast merchant, a convinced Presbyterian, a son of the twin traditions of the British Whigs and the American Revolution with their emphasis on human rights and ultimate freedom of action. Sinclair, a modest figure, has long been forgotten, but it was his finely constructed phrases which, in 1912, articulated eternal essential freedoms and thus gave him some claim to be modern Ulster's Thomas Jefferson.No one can read Sinclair's text, the text of Ulster's Solemn League and Covenant, without being struck by its masterly construction: concise in its wording; comprehensive in its scope; reasonable in its tone, yet conveying a sense of cool determination. It was a document which, given its content and tone, could be signed by a wide range of people with a clear conscience.
The Ulster Solemn League and Covenant stands in the tradition of the Scottish covenants and its author, Thomas Sinclair, was proud of his Ulster-Scots heritage. He was the leading Presbyterian layman of his day and a prominent Liberal who became a Liberal Unionist.