From
The Scot's Peerage1:
Robert Stewart, third son of King Robert II by Elizabeth Mure, his first wife, born in 1339, married first, by dispensation dated 9 September 1361, as her fourth husband, Margaret, Countess of Menteith, by which marriage he became by courtesy Earl of Menteith. He entered into an indenture with Isobel, Countess of Fife, relict of his elder brother Walter, dated at Perth, 30 March 1371, wherein she acknowledges him to be her lawful heir-apparent, and that, when the Earldom of Fife is recovered and the Countess has got possession of it, she will resign it into the King's hands for infeftment in his favour. In consequence of this he succeeded to that Earldom, and was styled Earl of Fife and Menteith. By Crown charter, dated 7 February 1372-3, the custody of the Castle of Stirling was committed to his care. In 1382 he was appointed Great Chamberlain of Scotland, which office he held till 1408, when he resigned it in favour of his son John, Earl of Buchan.
In 1385, in conjunction with the Earl of Douglas and a body of French auxiliaries under Jean de Vienne, Admiral of France, he invaded England with an army of 30,000 men, took the Castle of Wark, and ravaged the country from Berwick to Newcastle. On the advance of the Duke of Lancaster against him, he retired into Scotland, which was thereupon invaded by the English. The Earls of Fife and Douglas, along with Archibald, Lord of Galloway, thereupon invaded Cumberland as far as Cockermouth, spoiling the country between the Fells and the sea.
The Earl of Menteith made another successful invasion of England in 1388. His father. King Robert II, being now far advanced in years, and his elder brother, the Earl of Carrick, afterwards Robert iIII, being from bodily infirmity unable to take an active part in government, a parliament was called in which the Earl of Fife was by the Three Estates solemnly recognised on 1 December 1388 as guardian of the kingdom, in which office he continued after the death of his father and the accession of his elder brother, John, Earl of Carrick, to the throne, under the title of Robert III, in 1390.
Eight years after this, when the heir-apparent to the throne was created Duke of Rothesay, the Earl of Fife and Menteith, on 28 April 1398, was created Duke of Albany. The following year he had the pretended King Richard II placed under his custody. His nephew, the Duke of Rothesay, having been for some youthful excesses, by order of his father, King Robert III, seized and delivered into his safe-keeping, it has been alleged that he was most barbarously starved to death in Albany's Castle of Falkland, 27 March 1402. It is more likely, however, that he died of dysentery. A parliament was called and met at Edinburgh, 16 May 1402, to inquire into the fact, and Albany and the Earl of Douglas having confessed the imprisonment, imputing the death to divine providence, were acquitted of the charge and obtained a full remission under the Great Seal.
The following year the Regent assembled forces, took Innerwick from the English and saved Cocklaws Castle from being delivered up to the Percies by James de Gladstanes, who had agreed to surrender if not succoured in time. On 2 September 1403 the Earldom of Atholl, which had reverted to the Crown on the death of the Duke of Rothesay, was conferred on him in free regality during the lifetime of the King only, with a remainder to his son John in case of his predecease/ On the death of King Robert III.
In 1406, the Duke of Albany was constituted regent and governor of the realm of Scotland, his nephew James being a prisoner in England. When King Henry V was in France, in 1417, the regent raised an army to invade England and attack Berwick, but was forced to retire by the Dukes of Bedford and Exeter.
In 1419 he despatched his son John, Earl of Buchan, with a chosen army of 7000 men into France to assist the Dauphin against the English, and he concluded a long and active life of vigorous exertion at the Castle of Stirling, 2 September 1420, aged upwards of eighty. His body was interred in the Abbey Church of Dunfermline.
Wintoun and Bower draw his character in very flattering colours, and while he may not be the melodramatic villain described by Pinkerton neither was he, as represented by the writer of the Red Book of Menteith, the most perfect man who ever inhabited this world.
He married, first, Margaret, Countess of Menteith, only daughter of Sir John Graham and Mary, Countess of Menteith, widow of Sir John Moray, Lord of Bothwell, Thomas, thirteenth Earl of Mar, and Sir John Drummond of Concraig. By her, who died about 1380, he had issue.
Death
Robert died either 2nd or 3rd of September 1420.
Footnotes
[1]
The Scot's Peerage, James Balfour Paul, Vol 1, 1904, pages 146-148
Abt 1340 - 1420 (~ 80 years)
[1] 
