John Erskine, 23rd Earl of Mar, lived from 1675 to May 1732. An important landowner and politician, he played an key role in the Act of Union between Scotland and England in 1707; then led the Jacobite cause in the 1715 uprising. His frequent changes of sides led to him being known as "Bobbing John", and to his losing the trust of just about everyone. The wider picture in Scotland at the time is set out in our Historical Timeline.
Any discussion of John Erskine, 23rd Earl of Mar, has to start with a brief overview of how Scottish titles were awarded and recorded. It was quite common for a title, e.g. an Earldom, to be awarded more than once in history, with the second and subsequent "creations" taking place after the first "creation" had been extinguished, either through an inability of the holder to produce an heir, or because they crossed the king or queen of the day too sharply and had the title taken away ("attainted").
The confusion tends to arise because later creations would often, but not always, restart the count (e.g. "the 1st Earl of x") from scratch, meaning there could be several different "1st Earls of x" at different times in history. Yet on other occasions the background count of someone's order in the succession would continue across gaps between creations.
This matters because John Erskine, often nowadays referred to as the 23rd Earl of Mar, has also at times been referred to as the 11th Earl of Mar or the 6th Earl of Mar: it depends when, in the complex and ancient set of creations and re-creations of the Earldom of Mar, you start counting. With John Erskine, things become even more complicated because, after the failure of the 1715 uprising and his flight to France, his Earldom of Mar was attainted (only to be restored to a successor in 1824): but meanwhile, he was created the Jacobite Earl of Mar. This further twist is because the hopeful "James VIII/III", while in exile in France, created a range of titles in England and Scotland that were meant to come into effect once he had assumed power. He didn't, so they didn't.
Mar inherited his title, and debt-laden estates in Clackmannanshire, from his father in 1689. He went on to establish Alloa as a coal-mining centre, doing much to restore the family fortunes. Under Queen Anne, who ruled from 1702-14, Mar flourished, serving twice as Secretary of State for Scotland, while as a Commissioner for the Union in 1707 he played a key role in the Union of the Parliaments. After 1707 he became a Representative Peer for Scotland, served as Keeper of the Signet, and was appointed as a Privy Counsellor. Throughout this time, Mar was gaining a reputation for supporting either Whigs or Tories depending on what served him best at the time. By 1713 he had become disillusioned with the Act of Union and had proposed a Resolution to have it repealed. He lost. When George I arrived in England to take up his throne, Mar was serving in the Government as "Third Secretary for Great Britain".
Mar wrote George I a grovelling letter of welcome, in which he pledged his loyalty, but was then publicly snubbed by George. Mar swiftly decided to back a different horse, and on 1 September 1715 raised a standard for "King James VIII" at Braemar. He rapidly gathered an enthusiastic army of 10,000 men and started to gain considerable ground in northern Scotland. There were three main problems with all of this. The first was that Mar had neglected to tell James in advance of his planned uprising; the second was that he had failed to coordinate his actions with Jacobite uprisings that by coincidence occurred in England; and the third was that Mar was a very poor general. As a result, what was by far the best opportunity the Jacobites would ever have of regaining power was squandered.
On 13 November 1715, a large part of Mar's army advancing from Perth met a much smaller government army under John Campbell, the 2nd Duke of Argyll at the Battle of Sheriffmuir, north of Dunblane. Mar's forces probably just about won on the day, but he failed to take advantage of the open road that now lay to the south, and withdrew. Meanwhile, James Stuart was only able to reach Scotland on 22 December, when he landed at Peterhead: he was too late, the uprising was all but over. The Jacobites abandoned Perth on 31 January 1716, and on 4 February James Stuart and John Erskine, 23rd Earl of Mar, sailed out of Montrose, bound for France. Neither would ever return.
Mar tried hard to raise foreign support for the Jacobite cause, but in 1721 it emerged he was receiving a pension of £3500 per year from George I, and the Jacobites ceased to trust him. Many thought he had a hand in betraying to George a plot involving Bishop Francis Atterbury, in which the Hanoverian royal family would be taken prisoner, and James proclaimed King in London. Mar subsequently cut his links with the Jacobites, spending the rest of his life in Paris and in Aix-la-Chapelle, where he died in May 1732.